---
name: "CrtMathFnc"
section: "3tcl"
platform: "linux"
package: "tcl8.3-doc"
version: "8.3.5-13"
release: "Debian 5.0 (Lenny)"
platforms: ["linux"]
url: "https://new.carta.tech/CrtMathFnc/3tcl"
---

# CrtMathFnc(3tcl)

Define a new math function for expressions

```

```

## NAME

Tcl\_CreateMathFunc - Define a new math function for expressions

## SYNOPSIS

```
#include <tcl.h>

Tcl_CreateMathFunc(interp, name, numArgs, argTypes, proc, clientData)
```

## ARGUMENTS

- Tcl\_Interp *\*interp* (in)

  Interpreter in which new function will be defined.

- char *\*name* (in)

  Name for new function.

- int *numArgs* (in)

  Number of arguments to new function;  also gives size of *argTypes* array.

- Tcl\_ValueType *\*argTypes* (in)

  Points to an array giving the permissible types for each argument to function.

- Tcl\_MathProc *\*proc* (in)

  Procedure that implements the function.

- ClientData *clientData* (in)

  Arbitrary one-word value to pass to *proc* when it is invoked.

  ```

  ```

## DESCRIPTION

Tcl allows a number of mathematical functions to be used in expressions, such as **sin**, **cos**, and **hypot**. **Tcl\_CreateMathFunc** allows applications to add additional functions to those already provided by Tcl or to replace existing functions. *Name* is the name of the function as it will appear in expressions. If *name* doesn't already exist as a function then a new function is created.  If it does exist, then the existing function is replaced. *NumArgs* and *argTypes* describe the arguments to the function. Each entry in the *argTypes* array must be either TCL\_INT, TCL\_DOUBLE, or TCL\_EITHER to indicate whether the corresponding argument must be an integer, a double-precision floating value, or either, respectively.

Whenever the function is invoked in an expression Tcl will invoke *proc*.  *Proc* should have arguments and result that match the type **Tcl\_MathProc**:

```
typedef int Tcl_MathProc(
	ClientData clientData,
	Tcl_Interp *interp,
	Tcl_Value *args,
	Tcl_Value *resultPtr);
```

When *proc* is invoked the *clientData* and *interp* arguments will be the same as those passed to **Tcl\_CreateMathFunc**. *Args* will point to an array of *numArgs* Tcl\_Value structures, which describe the actual arguments to the function:

```
typedef struct Tcl_Value {
	Tcl_ValueType type;
	long intValue;
	double doubleValue;
} Tcl_Value;
```

The *type* field indicates the type of the argument and is either TCL\_INT or TCL\_DOUBLE. It will match the *argTypes* value specified for the function unless the *argTypes* value was TCL\_EITHER. Tcl converts the argument supplied in the expression to the type requested in *argTypes*, if that is necessary. Depending on the value of the *type* field, the *intValue* or *doubleValue* field will contain the actual value of the argument.

*Proc* should compute its result and store it either as an integer in *resultPtr-\>intValue* or as a floating value in *resultPtr-\>doubleValue*. It should set also *resultPtr-\>type* to either TCL\_INT or TCL\_DOUBLE to indicate which value was set. Under normal circumstances *proc* should return TCL\_OK. If an error occurs while executing the function, *proc* should return TCL\_ERROR and leave an error message in the interpreter's result.

## KEYWORDS

expression, mathematical function