---
name: "Pervasives"
section: "3o"
platform: "linux"
package: "ocaml-nox"
version: "4.05.0-11"
release: "Debian 10 (Buster)"
platforms: ["linux"]
url: "https://new.carta.tech/Pervasives"
---

# Pervasives(3o)

The initially opened module.

## NAME

Pervasives - The initially opened module.

## Module

Module   Pervasives

## Documentation

Module **Pervasives**\
  :  **sig end**

The initially opened module.

This module provides the basic operations over the built-in types (numbers, booleans, byte sequences, strings, exceptions, references, lists, arrays, input-output channels, ...).

This module is automatically opened at the beginning of each compilation. All components of this module can therefore be referred by their short name, without prefixing them by  **Pervasives** .

**===** **Exceptions** **===**

*val raise* :  **exn -\> 'a**

Raise the given exception value

*val raise\_notrace* :  **exn -\> 'a**

A faster version  **raise** which does not record the backtrace.

**Since** 4.02.0

*val invalid\_arg* :  **string -\> 'a**

Raise exception  **Invalid\_argument** with the given string.

*val failwith* :  **string -\> 'a**

Raise exception  **Failure** with the given string.

*exception Exit*

The  **Exit** exception is not raised by any library function.  It is provided for use in your programs.

**===** **Comparisons** **===**

*val (=)* :  **'a -\> 'a -\> bool**

**e1 = e2** tests for structural equality of  **e1** and  **e2** . Mutable structures (e.g. references and arrays) are equal if and only if their current contents are structurally equal, even if the two mutable objects are not the same physical object. Equality between functional values raises  **Invalid\_argument** . Equality between cyclic data structures may not terminate.

*val (\<\>)* :  **'a -\> 'a -\> bool**

Negation of  **Pervasives.(=)** .

*val (\<)* :  **'a -\> 'a -\> bool**

See  **Pervasives.(\>=)** .

*val (\>)* :  **'a -\> 'a -\> bool**

See  **Pervasives.(\>=)** .

*val (\<=)* :  **'a -\> 'a -\> bool**

See  **Pervasives.(\>=)** .

*val (\>=)* :  **'a -\> 'a -\> bool**

Structural ordering functions. These functions coincide with the usual orderings over integers, characters, strings, byte sequences and floating-point numbers, and extend them to a total ordering over all types. The ordering is compatible with  **( = )** . As in the case of  **( = )** , mutable structures are compared by contents. Comparison between functional values raises  **Invalid\_argument** . Comparison between cyclic structures may not terminate.

*val compare* :  **'a -\> 'a -\> int**

**compare x y** returns  **0** if  **x** is equal to  **y** , a negative integer if  **x** is less than  **y** , and a positive integer if  **x** is greater than  **y** .  The ordering implemented by  **compare** is compatible with the comparison predicates  **=** ,  **\<** and  **\>** defined above,  with one difference on the treatment of the float value **Pervasives.nan** .  Namely, the comparison predicates treat  **nan** as different from any other float value, including itself; while  **compare** treats  **nan** as equal to itself and less than any other float value.  This treatment of  **nan** ensures that  **compare** defines a total ordering relation.

**compare** applied to functional values may raise  **Invalid\_argument** . **compare** applied to cyclic structures may not terminate.

The  **compare** function can be used as the comparison function required by the  **Set.Make** and  **Map.Make** functors, as well as the  **List.sort** and  **Array.sort** functions.

*val min* :  **'a -\> 'a -\> 'a**

Return the smaller of the two arguments. The result is unspecified if one of the arguments contains the float value  **nan** .

*val max* :  **'a -\> 'a -\> 'a**

Return the greater of the two arguments. The result is unspecified if one of the arguments contains the float value  **nan** .

*val (==)* :  **'a -\> 'a -\> bool**

**e1 == e2** tests for physical equality of  **e1** and  **e2** . On mutable types such as references, arrays, byte sequences, records with mutable fields and objects with mutable instance variables, **e1 == e2** is true if and only if physical modification of  **e1** also affects  **e2** . On non-mutable types, the behavior of  **( == )** is implementation-dependent; however, it is guaranteed that **e1 == e2** implies  **compare e1 e2 = 0** .

*val (!=)* :  **'a -\> 'a -\> bool**

Negation of  **Pervasives.(==)** .

**===** **Boolean operations** **===**

*val not* :  **bool -\> bool**

The boolean negation.

*val (&&)* :  **bool -\> bool -\> bool**

The boolean 'and'. Evaluation is sequential, left-to-right: in  **e1 && e2** ,  **e1** is evaluated first, and if it returns  **false** , **e2** is not evaluated at all.

*val (&)* :  **bool -\> bool -\> bool**

**Deprecated.**

**Pervasives.(&&)** should be used instead.

*val (\|\|)* :  **bool -\> bool -\> bool**

The boolean 'or'. Evaluation is sequential, left-to-right: in  **e1 \|\| e2** ,  **e1** is evaluated first, and if it returns  **true** , **e2** is not evaluated at all.

*val (or)* :  **bool -\> bool -\> bool**

**Deprecated.**

**Pervasives.(\|\|)** should be used instead.

**===** **Debugging** **===**

*val \_\_LOC\_\_* :  **string**

**\_\_LOC\_\_** returns the location at which this expression appears in the file currently being parsed by the compiler, with the standard error format of OCaml: "File %S, line %d, characters %d-%d".

**Since** 4.02.0

*val \_\_FILE\_\_* :  **string**

**\_\_FILE\_\_** returns the name of the file currently being parsed by the compiler.

**Since** 4.02.0

*val \_\_LINE\_\_* :  **int**

**\_\_LINE\_\_** returns the line number at which this expression appears in the file currently being parsed by the compiler.

**Since** 4.02.0

*val \_\_MODULE\_\_* :  **string**

**\_\_MODULE\_\_** returns the module name of the file being parsed by the compiler.

**Since** 4.02.0

*val \_\_POS\_\_* :  **string \* int \* int \* int**

**\_\_POS\_\_** returns a tuple  **(file,lnum,cnum,enum)** , corresponding to the location at which this expression appears in the file currently being parsed by the compiler.  **file** is the current filename,  **lnum** the line number,  **cnum** the character position in the line and  **enum** the last character position in the line.

**Since** 4.02.0

*val \_\_LOC\_OF\_\_* :  **'a -\> string \* 'a**

**\_\_LOC\_OF\_\_ expr** returns a pair  **(loc, expr)** where  **loc** is the location of  **expr** in the file currently being parsed by the compiler, with the standard error format of OCaml: "File %S, line %d, characters %d-%d".

**Since** 4.02.0

*val \_\_LINE\_OF\_\_* :  **'a -\> int \* 'a**

**\_\_LINE\_\_ expr** returns a pair  **(line, expr)** , where  **line** is the line number at which the expression  **expr** appears in the file currently being parsed by the compiler.

**Since** 4.02.0

*val \_\_POS\_OF\_\_* :  **'a -\> (string \* int \* int \* int) \* 'a**

**\_\_POS\_OF\_\_ expr** returns a pair  **(loc,expr)** , where  **loc** is a tuple  **(file,lnum,cnum,enum)** corresponding to the location at which the expression  **expr** appears in the file currently being parsed by the compiler.  **file** is the current filename,  **lnum** the line number,  **cnum** the character position in the line and  **enum** the last character position in the line.

**Since** 4.02.0

**===** **Composition operators** **===**

*val (\|\>)* :  **'a -\> ('a -\> 'b) -\> 'b**

Reverse-application operator:  **x \|\> f \|\> g** is exactly equivalent to  **g (f (x))** .

**Since** 4.01

*val (@@)* :  **('a -\> 'b) -\> 'a -\> 'b**

Application operator:  **g @@ f @@ x** is exactly equivalent to **g (f (x))** .

**Since** 4.01

**===** **Integer arithmetic** **===**

**=== Integers are 31 bits wide (or 63 bits on 64-bit processors).** **All operations are taken modulo 2^{31} (or 2^{63}).** **They do not fail on overflow. ===**

*val (~-)* :  **int -\> int**

Unary negation. You can also write  **- e** instead of  **~- e** .

*val (~+)* :  **int -\> int**

Unary addition. You can also write  **+ e** instead of  **~+ e** .

**Since** 3.12.0

*val succ* :  **int -\> int**

**succ x** is  **x + 1** .

*val pred* :  **int -\> int**

**pred x** is  **x - 1** .

*val (+)* :  **int -\> int -\> int**

Integer addition.

*val (-)* :  **int -\> int -\> int**

Integer subtraction.

*val ( \* )* :  **int -\> int -\> int**

Integer multiplication.

*val (/)* :  **int -\> int -\> int**

Integer division. Raise  **Division\_by\_zero** if the second argument is 0. Integer division rounds the real quotient of its arguments towards zero. More precisely, if  **x \>= 0** and  **y \> 0** ,  **x / y** is the greatest integer less than or equal to the real quotient of  **x** by  **y** .  Moreover, **(- x) / y = x / (- y) = - (x / y)** .

*val (mod)* :  **int -\> int -\> int**

Integer remainder.  If  **y** is not zero, the result of  **x mod y** satisfies the following properties: **x = (x / y) \* y + x mod y** and **abs(x mod y) \<= abs(y) - 1** . If  **y = 0** ,  **x mod y** raises  **Division\_by\_zero** . Note that  **x mod y** is negative only if  **x \< 0** . Raise  **Division\_by\_zero** if  **y** is zero.

*val abs* :  **int -\> int**

Return the absolute value of the argument.  Note that this may be negative if the argument is  **min\_int** .

*val max\_int* :  **int**

The greatest representable integer.

*val min\_int* :  **int**

The smallest representable integer.

**===** **Bitwise operations** **===**

*val (land)* :  **int -\> int -\> int**

Bitwise logical and.

*val (lor)* :  **int -\> int -\> int**

Bitwise logical or.

*val (lxor)* :  **int -\> int -\> int**

Bitwise logical exclusive or.

*val lnot* :  **int -\> int**

Bitwise logical negation.

*val (lsl)* :  **int -\> int -\> int**

**n lsl m** shifts  **n** to the left by  **m** bits. The result is unspecified if  **m \< 0** or  **m \>= bitsize** , where  **bitsize** is  **32** on a 32-bit platform and **64** on a 64-bit platform.

*val (lsr)* :  **int -\> int -\> int**

**n lsr m** shifts  **n** to the right by  **m** bits. This is a logical shift: zeroes are inserted regardless of the sign of  **n** . The result is unspecified if  **m \< 0** or  **m \>= bitsize** .

*val (asr)* :  **int -\> int -\> int**

**n asr m** shifts  **n** to the right by  **m** bits. This is an arithmetic shift: the sign bit of  **n** is replicated. The result is unspecified if  **m \< 0** or  **m \>= bitsize** .

**===** **Floating-point arithmetic** **OCaml's floating-point numbers follow the** **IEEE 754 standard, using double precision (64 bits) numbers.** **Floating-point operations never raise an exception on overflow,** **underflow, division by zero, etc. Instead, special IEEE numbers** **are returned as appropriate, such as infinity for 1.0 /. 0.0,** **neg\_infinity for -1.0 /. 0.0, and nan ('not a number')** **for 0.0 /. 0.0. These special numbers then propagate through** **floating-point computations as expected: for instance,** **1.0 /. infinity is 0.0, and any arithmetic operation with nan** **as argument returns nan as result. ===**

*val (~-.)* :  **float -\> float**

Unary negation. You can also write  **-. e** instead of  **~-. e** .

*val (~+.)* :  **float -\> float**

Unary addition. You can also write  **+. e** instead of  **~+. e** .

**Since** 3.12.0

*val (+.)* :  **float -\> float -\> float**

Floating-point addition

*val (-.)* :  **float -\> float -\> float**

Floating-point subtraction

*val ( \*. )* :  **float -\> float -\> float**

Floating-point multiplication

*val (/.)* :  **float -\> float -\> float**

Floating-point division.

*val ( \*\* )* :  **float -\> float -\> float**

Exponentiation.

*val sqrt* :  **float -\> float**

Square root.

*val exp* :  **float -\> float**

Exponential.

*val log* :  **float -\> float**

Natural logarithm.

*val log10* :  **float -\> float**

Base 10 logarithm.

*val expm1* :  **float -\> float**

**expm1 x** computes  **exp x -. 1.0** , giving numerically-accurate results even if  **x** is close to  **0.0** .

**Since** 3.12.0

*val log1p* :  **float -\> float**

**log1p x** computes  **log(1.0 +. x)** (natural logarithm), giving numerically-accurate results even if  **x** is close to  **0.0** .

**Since** 3.12.0

*val cos* :  **float -\> float**

Cosine.  Argument is in radians.

*val sin* :  **float -\> float**

Sine.  Argument is in radians.

*val tan* :  **float -\> float**

Tangent.  Argument is in radians.

*val acos* :  **float -\> float**

Arc cosine.  The argument must fall within the range  **\[-1.0, 1.0\]** . Result is in radians and is between  **0.0** and  **pi** .

*val asin* :  **float -\> float**

Arc sine.  The argument must fall within the range  **\[-1.0, 1.0\]** . Result is in radians and is between  **-pi/2** and  **pi/2** .

*val atan* :  **float -\> float**

Arc tangent. Result is in radians and is between  **-pi/2** and  **pi/2** .

*val atan2* :  **float -\> float -\> float**

**atan2 y x** returns the arc tangent of  **y /. x** .  The signs of  **x** and  **y** are used to determine the quadrant of the result. Result is in radians and is between  **-pi** and  **pi** .

*val hypot* :  **float -\> float -\> float**

**hypot x y** returns  **sqrt(x \*. x + y \*. y)** , that is, the length of the hypotenuse of a right-angled triangle with sides of length **x** and  **y** , or, equivalently, the distance of the point  **(x,y)** to origin.  If one of  **x** or  **y** is infinite, returns  **infinity** even if the other is  **nan** .

**Since** 4.00.0

*val cosh* :  **float -\> float**

Hyperbolic cosine.  Argument is in radians.

*val sinh* :  **float -\> float**

Hyperbolic sine.  Argument is in radians.

*val tanh* :  **float -\> float**

Hyperbolic tangent.  Argument is in radians.

*val ceil* :  **float -\> float**

Round above to an integer value. **ceil f** returns the least integer value greater than or equal to  **f** . The result is returned as a float.

*val floor* :  **float -\> float**

Round below to an integer value. **floor f** returns the greatest integer value less than or equal to  **f** . The result is returned as a float.

*val abs\_float* :  **float -\> float**

**abs\_float f** returns the absolute value of  **f** .

*val copysign* :  **float -\> float -\> float**

**copysign x y** returns a float whose absolute value is that of  **x** and whose sign is that of  **y** .  If  **x** is  **nan** , returns  **nan** . If  **y** is  **nan** , returns either  **x** or  **-. x** , but it is not specified which.

**Since** 4.00.0

*val mod\_float* :  **float -\> float -\> float**

**mod\_float a b** returns the remainder of  **a** with respect to **b** .  The returned value is  **a -. n \*. b** , where  **n** is the quotient  **a /. b** rounded towards zero to an integer.

*val frexp* :  **float -\> float \* int**

**frexp f** returns the pair of the significant and the exponent of  **f** .  When  **f** is zero, the significant  **x** and the exponent  **n** of  **f** are equal to zero.  When  **f** is non-zero, they are defined by **f = x \*. 2 \*\* n** and  **0.5 \<= x \< 1.0** .

*val ldexp* :  **float -\> int -\> float**

**ldexp x n** returns  **x \*. 2 \*\* n** .

*val modf* :  **float -\> float \* float**

**modf f** returns the pair of the fractional and integral part of  **f** .

*val float* :  **int -\> float**

Same as  **Pervasives.float\_of\_int** .

*val float\_of\_int* :  **int -\> float**

Convert an integer to floating-point.

*val truncate* :  **float -\> int**

Same as  **Pervasives.int\_of\_float** .

*val int\_of\_float* :  **float -\> int**

Truncate the given floating-point number to an integer. The result is unspecified if the argument is  **nan** or falls outside the range of representable integers.

*val infinity* :  **float**

Positive infinity.

*val neg\_infinity* :  **float**

Negative infinity.

*val nan* :  **float**

A special floating-point value denoting the result of an undefined operation such as  **0.0 /. 0.0** .  Stands for 'not a number'.  Any floating-point operation with  **nan** as argument returns  **nan** as result.  As for floating-point comparisons, **=** ,  **\<** ,  **\<=** ,  **\>** and  **\>=** return  **false** and  **\<\>** returns  **true** if one or both of their arguments is  **nan** .

*val max\_float* :  **float**

The largest positive finite value of type  **float** .

*val min\_float* :  **float**

The smallest positive, non-zero, non-denormalized value of type  **float** .

*val epsilon\_float* :  **float**

The difference between  **1.0** and the smallest exactly representable floating-point number greater than  **1.0** .

*type fpclass* =\
  \| FP\_normal  (\* Normal number, none of the below\
  \*)\
  \| FP\_subnormal  (\* Number very close to 0.0, has reduced precision\
  \*)\
  \| FP\_zero  (\* Number is 0.0 or -0.0\
  \*)\
  \| FP\_infinite  (\* Number is positive or negative infinity\
  \*)\
  \| FP\_nan  (\* Not a number: result of an undefined operation\
  \*)

The five classes of floating-point numbers, as determined by the  **Pervasives.classify\_float** function.

*val classify\_float* :  **float -\> fpclass**

Return the class of the given floating-point number: normal, subnormal, zero, infinite, or not a number.

**===** **String operations** **More string operations are provided in module String. ===**

*val (^)* :  **string -\> string -\> string**

String concatenation.

**===** **Character operations** **More character operations are provided in module Char. ===**

*val int\_of\_char* :  **char -\> int**

Return the ASCII code of the argument.

*val char\_of\_int* :  **int -\> char**

Return the character with the given ASCII code. Raise  **Invalid\_argument char\_of\_int** if the argument is outside the range 0--255.

**===** **Unit operations** **===**

*val ignore* :  **'a -\> unit**

Discard the value of its argument and return  **()** . For instance,  **ignore(f x)** discards the result of the side-effecting function  **f** .  It is equivalent to **f x; ()** , except that the latter may generate a compiler warning; writing  **ignore(f x)** instead avoids the warning.

**===** **String conversion functions** **===**

*val string\_of\_bool* :  **bool -\> string**

Return the string representation of a boolean. As the returned values may be shared, the user should not modify them directly.

*val bool\_of\_string* :  **string -\> bool**

Convert the given string to a boolean. Raise  **Invalid\_argument bool\_of\_string** if the string is not **true** or  **false** .

*val bool\_of\_string\_opt* :  **string -\> bool option**

Convert the given string to a boolean. Return  **None** if the string is not **true** or  **false** .

**Since** 4.05

*val string\_of\_int* :  **int -\> string**

Return the string representation of an integer, in decimal.

*val int\_of\_string* :  **string -\> int**

Convert the given string to an integer. The string is read in decimal (by default), in hexadecimal (if it begins with  **0x** or  **0X** ), in octal (if it begins with  **0o** or  **0O** ), or in binary (if it begins with  **0b** or  **0B** ). The  **\_** (underscore) character can appear anywhere in the string and is ignored. Raise  **Failure int\_of\_string** if the given string is not a valid representation of an integer, or if the integer represented exceeds the range of integers representable in type  **int** .

*val int\_of\_string\_opt* :  **string -\> int option**

Same as  **int\_of\_string** , but returs  **None** instead of raising.

**Since** 4.05

*val string\_of\_float* :  **float -\> string**

Return the string representation of a floating-point number.

*val float\_of\_string* :  **string -\> float**

Convert the given string to a float.  The string is read in decimal (by default) or in hexadecimal (marked by  **0x** or  **0X** ). The format of decimal floating-point numbers is **\[-\] dd.ddd (e\|E) \[+\|-\] dd** , where  **d** stands for a decimal digit. The format of hexadecimal floating-point numbers is **\[-\] 0(x\|X) hh.hhh (p\|P) \[+\|-\] dd** , where  **h** stands for an hexadecimal digit and  **d** for a decimal digit. In both cases, at least one of the integer and fractional parts must be given; the exponent part is optional. The  **\_** (underscore) character can appear anywhere in the string and is ignored. Depending on the execution platforms, other representations of floating-point numbers can be accepted, but should not be relied upon. Raise  **Failure float\_of\_string** if the given string is not a valid representation of a float.

*val float\_of\_string\_opt* :  **string -\> float option**

Same as  **float\_of\_string** , but returns  **None** instead of raising.

**Since** 4.05

**===** **Pair operations** **===**

*val fst* :  **'a \* 'b -\> 'a**

Return the first component of a pair.

*val snd* :  **'a \* 'b -\> 'b**

Return the second component of a pair.

**===** **List operations** **More list operations are provided in module List. ===**

*val (@)* :  **'a list -\> 'a list -\> 'a list**

List concatenation.  Not tail-recursive (length of the first argument).

**===** **Input/output** **Note: all input/output functions can raise Sys\_error when the system** **calls they invoke fail. ===**

*type in\_channel*

The type of input channel.

*type out\_channel*

The type of output channel.

*val stdin* :  **in\_channel**

The standard input for the process.

*val stdout* :  **out\_channel**

The standard output for the process.

*val stderr* :  **out\_channel**

The standard error output for the process.

**===** **Output functions on standard output** **===**

*val print\_char* :  **char -\> unit**

Print a character on standard output.

*val print\_string* :  **string -\> unit**

Print a string on standard output.

*val print\_bytes* :  **bytes -\> unit**

Print a byte sequence on standard output.

**Since** 4.02.0

*val print\_int* :  **int -\> unit**

Print an integer, in decimal, on standard output.

*val print\_float* :  **float -\> unit**

Print a floating-point number, in decimal, on standard output.

*val print\_endline* :  **string -\> unit**

Print a string, followed by a newline character, on standard output and flush standard output.

*val print\_newline* :  **unit -\> unit**

Print a newline character on standard output, and flush standard output. This can be used to simulate line buffering of standard output.

**===** **Output functions on standard error** **===**

*val prerr\_char* :  **char -\> unit**

Print a character on standard error.

*val prerr\_string* :  **string -\> unit**

Print a string on standard error.

*val prerr\_bytes* :  **bytes -\> unit**

Print a byte sequence on standard error.

**Since** 4.02.0

*val prerr\_int* :  **int -\> unit**

Print an integer, in decimal, on standard error.

*val prerr\_float* :  **float -\> unit**

Print a floating-point number, in decimal, on standard error.

*val prerr\_endline* :  **string -\> unit**

Print a string, followed by a newline character on standard error and flush standard error.

*val prerr\_newline* :  **unit -\> unit**

Print a newline character on standard error, and flush standard error.

**===** **Input functions on standard input** **===**

*val read\_line* :  **unit -\> string**

Flush standard output, then read characters from standard input until a newline character is encountered. Return the string of all characters read, without the newline character at the end.

*val read\_int* :  **unit -\> int**

Flush standard output, then read one line from standard input and convert it to an integer. Raise  **Failure int\_of\_string** if the line read is not a valid representation of an integer.

*val read\_int\_opt* :  **unit -\> int option**

Same as  **read\_int\_opt** , but returs  **None** instead of raising.

**Since** 4.05

*val read\_float* :  **unit -\> float**

Flush standard output, then read one line from standard input and convert it to a floating-point number. The result is unspecified if the line read is not a valid representation of a floating-point number.

*val read\_float\_opt* :  **unit -\> float option**

Flush standard output, then read one line from standard input and convert it to a floating-point number. Returns  **None** if the line read is not a valid representation of a floating-point number.

**Since** 4.05.0

**===** **General output functions** **===**

*type open\_flag* =\
  \| Open\_rdonly  (\* open for reading.\
  \*)\
  \| Open\_wronly  (\* open for writing.\
  \*)\
  \| Open\_append  (\* open for appending: always write at end of file.\
  \*)\
  \| Open\_creat  (\* create the file if it does not exist.\
  \*)\
  \| Open\_trunc  (\* empty the file if it already exists.\
  \*)\
  \| Open\_excl  (\* fail if Open\_creat and the file already exists.\
  \*)\
  \| Open\_binary  (\* open in binary mode (no conversion).\
  \*)\
  \| Open\_text  (\* open in text mode (may perform conversions).\
  \*)\
  \| Open\_nonblock  (\* open in non-blocking mode.\
  \*)

Opening modes for  **Pervasives.open\_out\_gen** and **Pervasives.open\_in\_gen** .

*val open\_out* :  **string -\> out\_channel**

Open the named file for writing, and return a new output channel on that file, positioned at the beginning of the file. The file is truncated to zero length if it already exists. It is created if it does not already exists.

*val open\_out\_bin* :  **string -\> out\_channel**

Same as  **Pervasives.open\_out** , but the file is opened in binary mode, so that no translation takes place during writes. On operating systems that do not distinguish between text mode and binary mode, this function behaves like  **Pervasives.open\_out** .

*val open\_out\_gen* :  **open\_flag list -\> int -\> string -\> out\_channel**

**open\_out\_gen mode perm filename** opens the named file for writing, as described above. The extra argument  **mode** specifies the opening mode. The extra argument  **perm** specifies the file permissions, in case the file must be created. **Pervasives.open\_out** and  **Pervasives.open\_out\_bin** are special cases of this function.

*val flush* :  **out\_channel -\> unit**

Flush the buffer associated with the given output channel, performing all pending writes on that channel. Interactive programs must be careful about flushing standard output and standard error at the right time.

*val flush\_all* :  **unit -\> unit**

Flush all open output channels; ignore errors.

*val output\_char* :  **out\_channel -\> char -\> unit**

Write the character on the given output channel.

*val output\_string* :  **out\_channel -\> string -\> unit**

Write the string on the given output channel.

*val output\_bytes* :  **out\_channel -\> bytes -\> unit**

Write the byte sequence on the given output channel.

**Since** 4.02.0

*val output* :  **out\_channel -\> bytes -\> int -\> int -\> unit**

**output oc buf pos len** writes  **len** characters from byte sequence  **buf** , starting at offset  **pos** , to the given output channel  **oc** . Raise  **Invalid\_argument output** if  **pos** and  **len** do not designate a valid range of  **buf** .

*val output\_substring* :  **out\_channel -\> string -\> int -\> int -\> unit**

Same as  **output** but take a string as argument instead of a byte sequence.

**Since** 4.02.0

*val output\_byte* :  **out\_channel -\> int -\> unit**

Write one 8-bit integer (as the single character with that code) on the given output channel. The given integer is taken modulo 256.

*val output\_binary\_int* :  **out\_channel -\> int -\> unit**

Write one integer in binary format (4 bytes, big-endian) on the given output channel. The given integer is taken modulo 2^{32. The only reliable way to read it back is through the **Pervasives.input\_binary\_int** function. The format is compatible across all machines for a given version of OCaml.

*val output\_value* :  **out\_channel -\> 'a -\> unit**

Write the representation of a structured value of any type to a channel. Circularities and sharing inside the value are detected and preserved. The object can be read back, by the function  **Pervasives.input\_value** . See the description of module **Marshal** for more information.  **Pervasives.output\_value** is equivalent to  **Marshal.to\_channel** with an empty list of flags.

*val seek\_out* :  **out\_channel -\> int -\> unit**

**seek\_out chan pos** sets the current writing position to  **pos** for channel  **chan** . This works only for regular files. On files of other kinds (such as terminals, pipes and sockets), the behavior is unspecified.

*val pos\_out* :  **out\_channel -\> int**

Return the current writing position for the given channel.  Does not work on channels opened with the  **Open\_append** flag (returns unspecified results).

*val out\_channel\_length* :  **out\_channel -\> int**

Return the size (number of characters) of the regular file on which the given channel is opened.  If the channel is opened on a file that is not a regular file, the result is meaningless.

*val close\_out* :  **out\_channel -\> unit**

Close the given channel, flushing all buffered write operations. Output functions raise a  **Sys\_error** exception when they are applied to a closed output channel, except  **close\_out** and  **flush** , which do nothing when applied to an already closed channel. Note that  **close\_out** may raise  **Sys\_error** if the operating system signals an error when flushing or closing.

*val close\_out\_noerr* :  **out\_channel -\> unit**

Same as  **close\_out** , but ignore all errors.

*val set\_binary\_mode\_out* :  **out\_channel -\> bool -\> unit**

**set\_binary\_mode\_out oc true** sets the channel  **oc** to binary mode: no translations take place during output. **set\_binary\_mode\_out oc false** sets the channel  **oc** to text mode: depending on the operating system, some translations may take place during output.  For instance, under Windows, end-of-lines will be translated from  **\\n** to  **\\r\\n** . This function has no effect under operating systems that do not distinguish between text mode and binary mode.

**===** **General input functions** **===**

*val open\_in* :  **string -\> in\_channel**

Open the named file for reading, and return a new input channel on that file, positioned at the beginning of the file.

*val open\_in\_bin* :  **string -\> in\_channel**

Same as  **Pervasives.open\_in** , but the file is opened in binary mode, so that no translation takes place during reads. On operating systems that do not distinguish between text mode and binary mode, this function behaves like  **Pervasives.open\_in** .

*val open\_in\_gen* :  **open\_flag list -\> int -\> string -\> in\_channel**

**open\_in\_gen mode perm filename** opens the named file for reading, as described above. The extra arguments **mode** and  **perm** specify the opening mode and file permissions. **Pervasives.open\_in** and  **Pervasives.open\_in\_bin** are special cases of this function.

*val input\_char* :  **in\_channel -\> char**

Read one character from the given input channel. Raise  **End\_of\_file** if there are no more characters to read.

*val input\_line* :  **in\_channel -\> string**

Read characters from the given input channel, until a newline character is encountered. Return the string of all characters read, without the newline character at the end. Raise  **End\_of\_file** if the end of the file is reached at the beginning of line.

*val input* :  **in\_channel -\> bytes -\> int -\> int -\> int**

**input ic buf pos len** reads up to  **len** characters from the given channel  **ic** , storing them in byte sequence  **buf** , starting at character number  **pos** . It returns the actual number of characters read, between 0 and **len** (inclusive). A return value of 0 means that the end of file was reached. A return value between 0 and  **len** exclusive means that not all requested  **len** characters were read, either because no more characters were available at that time, or because the implementation found it convenient to do a partial read; **input** must be called again to read the remaining characters, if desired.  (See also  **Pervasives.really\_input** for reading exactly  **len** characters.) Exception  **Invalid\_argument input** is raised if  **pos** and  **len** do not designate a valid range of  **buf** .

*val really\_input* :  **in\_channel -\> bytes -\> int -\> int -\> unit**

**really\_input ic buf pos len** reads  **len** characters from channel  **ic** , storing them in byte sequence  **buf** , starting at character number  **pos** . Raise  **End\_of\_file** if the end of file is reached before  **len** characters have been read. Raise  **Invalid\_argument really\_input** if **pos** and  **len** do not designate a valid range of  **buf** .

*val really\_input\_string* :  **in\_channel -\> int -\> string**

**really\_input\_string ic len** reads  **len** characters from channel  **ic** and returns them in a new string. Raise  **End\_of\_file** if the end of file is reached before  **len** characters have been read.

**Since** 4.02.0

*val input\_byte* :  **in\_channel -\> int**

Same as  **Pervasives.input\_char** , but return the 8-bit integer representing the character. Raise  **End\_of\_file** if an end of file was reached.

*val input\_binary\_int* :  **in\_channel -\> int**

Read an integer encoded in binary format (4 bytes, big-endian) from the given input channel. See  **Pervasives.output\_binary\_int** . Raise  **End\_of\_file** if an end of file was reached while reading the integer.

*val input\_value* :  **in\_channel -\> 'a**

Read the representation of a structured value, as produced by  **Pervasives.output\_value** , and return the corresponding value. This function is identical to  **Marshal.from\_channel** ; see the description of module  **Marshal** for more information, in particular concerning the lack of type safety.

*val seek\_in* :  **in\_channel -\> int -\> unit**

**seek\_in chan pos** sets the current reading position to  **pos** for channel  **chan** . This works only for regular files. On files of other kinds, the behavior is unspecified.

*val pos\_in* :  **in\_channel -\> int**

Return the current reading position for the given channel.

*val in\_channel\_length* :  **in\_channel -\> int**

Return the size (number of characters) of the regular file on which the given channel is opened.  If the channel is opened on a file that is not a regular file, the result is meaningless. The returned size does not take into account the end-of-line translations that can be performed when reading from a channel opened in text mode.

*val close\_in* :  **in\_channel -\> unit**

Close the given channel.  Input functions raise a  **Sys\_error** exception when they are applied to a closed input channel, except  **close\_in** , which does nothing when applied to an already closed channel.

*val close\_in\_noerr* :  **in\_channel -\> unit**

Same as  **close\_in** , but ignore all errors.

*val set\_binary\_mode\_in* :  **in\_channel -\> bool -\> unit**

**set\_binary\_mode\_in ic true** sets the channel  **ic** to binary mode: no translations take place during input. **set\_binary\_mode\_out ic false** sets the channel  **ic** to text mode: depending on the operating system, some translations may take place during input.  For instance, under Windows, end-of-lines will be translated from  **\\r\\n** to  **\\n** . This function has no effect under operating systems that do not distinguish between text mode and binary mode.

**===** **Operations on large files** **===**

*module LargeFile :* **sig end**

Operations on large files. This sub-module provides 64-bit variants of the channel functions that manipulate file positions and file sizes.  By representing positions and sizes by 64-bit integers (type  **int64** ) instead of regular integers (type  **int** ), these alternate functions allow operating on files whose sizes are greater than  **max\_int** .

**===** **References** **===**

*type* **'a** *ref* = {

**mutable** contents :  **'a** ;\
  }

The type of references (mutable indirection cells) containing a value of type  **'a** .

*val ref* :  **'a -\> 'a ref**

Return a fresh reference containing the given value.

*val (!)* :  **'a ref -\> 'a**

**!r** returns the current contents of reference  **r** . Equivalent to  **fun r -\> r.contents** .

*val (:=)* :  **'a ref -\> 'a -\> unit**

**r := a** stores the value of  **a** in reference  **r** . Equivalent to  **fun r v -\> r.contents \<- v** .

*val incr* :  **int ref -\> unit**

Increment the integer contained in the given reference. Equivalent to  **fun r -\> r := succ !r** .

*val decr* :  **int ref -\> unit**

Decrement the integer contained in the given reference. Equivalent to  **fun r -\> r := pred !r** .

**===** **Result type** **===**

*type* **('a, 'b)** *result* =\
  \| Ok **of** **'a**\
  \| Error **of** **'b**

**Since** 4.03.0

**===** **Operations on format strings** **===**

**=== Format strings are character strings with special lexical conventions** **that defines the functionality of formatted input/output functions. Format** **strings are used to read data with formatted input functions from module** **Scanf and to print data with formatted output functions from modules** **Printf and Format.** **Format strings are made of three kinds of entities:** **- conversions specifications, introduced by the special character '%'** **followed by one or more characters specifying what kind of argument to** **read or print,** **- formatting indications, introduced by the special character '@'** **followed by one or more characters specifying how to read or print the** **argument,** **- plain characters that are regular characters with usual lexical** **conventions. Plain characters specify string literals to be read in the** **input or printed in the output.** **There is an additional lexical rule to escape the special characters '%'** **and '@' in format strings: if a special character follows a '%'** **character, it is treated as a plain character. In other words, %% is** **considered as a plain '%' and %@ as a plain '@'.** **For more information about conversion specifications and formatting** **indications available, read the documentation of modules Scanf,** **Printf and Format. ===**

**=== Format strings have a general and highly polymorphic type** **('a, 'b, 'c, 'd, 'e, 'f) format6.** **The two simplified types, format and format4 below are** **included for backward compatibility with earlier releases of** **OCaml.** **The meaning of format string type parameters is as follows:** **- 'a is the type of the parameters of the format for formatted output** **functions (printf-style functions);** **'a is the type of the values read by the format for formatted input** **functions (scanf-style functions).** **- 'b is the type of input source for formatted input functions and the** **type of output target for formatted output functions.** **For printf-style functions from module Printf, 'b is typically** **out\_channel;** **for printf-style functions from module Format, 'b is typically** **Format.formatter;** **for scanf-style functions from module Scanf, 'b is typically** **Scanf.Scanning.in\_channel.** **Type argument 'b is also the type of the first argument given to** **user's defined printing functions for %a and %t conversions,** **and user's defined reading functions for %r conversion.** **- 'c is the type of the result of the %a and %t printing** **functions, and also the type of the argument transmitted to the** **first argument of kprintf-style functions or to the** **kscanf-style functions.** **- 'd is the type of parameters for the scanf-style functions.** **- 'e is the type of the receiver function for the scanf-style functions.** **- 'f is the final result type of a formatted input/output function** **invocation: for the printf-style functions, it is typically unit;** **for the scanf-style functions, it is typically the result type of the** **receiver function.** **===**

*type* **('a, 'b, 'c, 'd, 'e, 'f)** *format6* =  **('a, 'b, 'c, 'd, 'e, 'f) CamlinternalFormatBasics.format6**

*type* **('a, 'b, 'c, 'd)** *format4* =  **('a, 'b, 'c, 'c, 'c, 'd) format6**

*type* **('a, 'b, 'c)** *format* =  **('a, 'b, 'c, 'c) format4**

*val string\_of\_format* :  **('a, 'b, 'c, 'd, 'e, 'f) format6 -\> string**

Converts a format string into a string.

*val format\_of\_string* :  **('a, 'b, 'c, 'd, 'e, 'f) format6 -\>** **('a, 'b, 'c, 'd, 'e, 'f) format6**

**format\_of\_string s** returns a format string read from the string literal  **s** . Note:  **format\_of\_string** can not convert a string argument that is not a literal. If you need this functionality, use the more general **Scanf.format\_from\_string** function.

*val (^^)* :  **('a, 'b, 'c, 'd, 'e, 'f) format6 -\>** **('f, 'b, 'c, 'e, 'g, 'h) format6 -\>** **('a, 'b, 'c, 'd, 'g, 'h) format6**

**f1 ^^ f2** catenates format strings  **f1** and  **f2** . The result is a format string that behaves as the concatenation of format strings  **f1** and **f2** : in case of formatted output, it accepts arguments from  **f1** , then arguments from  **f2** ; in case of formatted input, it returns results from **f1** , then results from  **f2** .

**===** **Program termination** **===**

*val exit* :  **int -\> 'a**

Terminate the process, returning the given status code to the operating system: usually 0 to indicate no errors, and a small positive integer to indicate failure. All open output channels are flushed with  **flush\_all** . An implicit  **exit 0** is performed each time a program terminates normally.  An implicit  **exit 2** is performed if the program terminates early because of an uncaught exception.

*val at\_exit* :  **(unit -\> unit) -\> unit**

Register the given function to be called at program termination time. The functions registered with  **at\_exit** will be called when the program executes  **Pervasives.exit** , or terminates, either normally or because of an uncaught exception. The functions are called in 'last in, first out' order: the function most recently added with  **at\_exit** is called first.