---
name: "StringObj"
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/StringObj/3tcl"
---

# StringObj(3tcl)

manipulate Tcl objects as strings

```

```

## NAME

Tcl\_NewStringObj, Tcl\_NewUnicodeObj, Tcl\_SetStringObj, Tcl\_SetUnicodeObj, Tcl\_GetStringFromObj, Tcl\_GetString, Tcl\_GetUnicode, Tcl\_GetUniChar, Tcl\_GetCharLength, Tcl\_GetRange, Tcl\_AppendToObj, Tcl\_AppendUnicodeToObj, Tcl\_AppendStringsToObj, Tcl\_AppendStringsToObjVA, Tcl\_AppendObjToObj, Tcl\_SetObjLength, Tcl\_ConcatObj - manipulate Tcl objects as strings

## SYNOPSIS

```
#include <tcl.h>

Tcl_Obj *
Tcl_NewStringObj(bytes, length)

Tcl_Obj *
Tcl_NewUnicodeObj(unicode, numChars)

void
Tcl_SetStringObj(objPtr, bytes, length)

void
Tcl_SetUnicodeObj(objPtr, unicode, numChars)

char *
Tcl_GetStringFromObj(objPtr, lengthPtr)

char *
Tcl_GetString(objPtr)

Tcl_UniChar *
Tcl_GetUnicode(objPtr)

Tcl_UniChar
Tcl_GetUniChar(objPtr, index)

int
Tcl_GetCharLength(objPtr)

Tcl_Obj *
Tcl_GetRange(objPtr, first, last)

void
Tcl_AppendToObj(objPtr, bytes, length)

void
Tcl_AppendUnicodeToObj(objPtr, unicode, numChars)

void
Tcl_AppendObjToObj(objPtr, appendObjPtr)

void
Tcl_AppendStringsToObj(objPtr, string, string, ... (char *) NULL)

void
Tcl_AppendStringsToObjVA(objPtr, argList)

void
Tcl_SetObjLength(objPtr, newLength)

Tcl_Obj *
Tcl_ConcatObj(objc, objv)
```

## ARGUMENTS

- char *\*bytes* (in)

  Points to the first byte of an array of bytes used to set or append to a string object. This byte array may contain embedded null bytes unless *length* is negative.

- int *length* (in)

  The number of bytes to copy from *bytes* when initializing, setting, or appending to a string object. If negative, all bytes up to the first null are used.

- Tcl\_UniChar *\*unicode* (in)

  Points to the first byte of an array of Unicode characters used to set or append to a string object. This byte array may contain embedded null characters unless *numChars* is negative.

- int *numChars* (in)

  The number of Unicode characters to copy from *unicode* when initializing, setting, or appending to a string object. If negative, all characters up to the first null character are used.

- int *index* (in)

  The index of the Unicode character to return.

- int *first* (in)

  The index of the first Unicode character in the Unicode range to be returned as a new object.

- int *last* (in)

  The index of the last Unicode character in the Unicode range to be returned as a new object.

- Tcl\_Obj *\*objPtr* (in/out)

  Points to an object to manipulate.

- Tcl\_Obj *\*appendObjPtr* (in)

  The object to append to *objPtr* in **Tcl\_AppendObjToObj**.

- int *\*lengthPtr* (out)

  If non-NULL, the location where **Tcl\_GetStringFromObj** will store the the length of an object's string representation.

- char *\*string* (in)

  Null-terminated string value to append to *objPtr*.

- va\_list *argList* (in)

  An argument list which must have been initialised using **TCL\_VARARGS\_START**, and cleared using **va\_end**.

- int *newLength* (in)

  New length for the string value of *objPtr*, not including the final NULL character.

- int *objc* (in)

  The number of elements to concatenate.

- Tcl\_Obj *\*objv\[\]* (in)

  The array of objects to concatenate.

  ```

  ```

## DESCRIPTION

The procedures described in this manual entry allow Tcl objects to be manipulated as string values.  They use the internal representation of the object to store additional information to make the string manipulations more efficient.  In particular, they make a series of append operations efficient by allocating extra storage space for the string so that it doesn't have to be copied for each append. Also, indexing and length computations are optimized because the Unicode string representation is calculated and cached as needed.

**Tcl\_NewStringObj** and **Tcl\_SetStringObj** create a new object or modify an existing object to hold a copy of the string given by *bytes* and *length*.  **Tcl\_NewUnicodeObj** and **Tcl\_SetUnicodeObj** create a new object or modify an existing object to hold a copy of the Unicode string given by *unicode* and *numChars*.  **Tcl\_NewStringObj** and **Tcl\_NewUnicodeObj** return a pointer to a newly created object with reference count zero. All four procedures set the object to hold a copy of the specified string.  **Tcl\_SetStringObj** and **Tcl\_SetUnicodeObj** free any old string representation as well as any old internal representation of the object.

**Tcl\_GetStringFromObj** and **Tcl\_GetString** return an object's string representation.  This is given by the returned byte pointer and (for **Tcl\_GetStringFromObj**) length, which is stored in *lengthPtr* if it is non-NULL.  If the object's UTF string representation is invalid (its byte pointer is NULL), the string representation is regenerated from the object's internal representation.  The storage referenced by the returned byte pointer is owned by the object manager and should not be modified by the caller.  The procedure **Tcl\_GetString** is used in the common case where the caller does not need the length of the string representation.

**Tcl\_GetUnicode** returns an object's value as a Unicode string. **Tcl\_GetUniChar** returns the *index*'th character in the object's Unicode representation.

**Tcl\_GetRange** returns a newly created object comprised of the characters between *first* and *last* (inclusive) in the object's Unicode representation.  If the object's Unicode representation is invalid, the Unicode representation is regenerated from the object's string representation.

**Tcl\_GetCharLength** returns the number of characters (as opposed to bytes) in the string object.

**Tcl\_AppendToObj** appends the data given by *bytes* and *length* to the string representation of the object specified by *objPtr*.  If the object has an invalid string representation, then an attempt is made to convert *bytes* is to the Unicode format.  If the conversion is successful, then the converted form of *bytes* is appended to the object's Unicode representation. Otherwise, the object's Unicode representation is invalidated and converted to the UTF format, and *bytes* is appended to the object's new string representation.

**Tcl\_AppendUnicodeToObj** appends the Unicode string given by *unicode* and *numChars* to the object specified by *objPtr*.  If the object has an invalid Unicode representation, then *unicode* is converted to the UTF format and appended to the object's string representation.  Appends are optimized to handle repeated appends relatively efficiently (it overallocates the string or Unicode space to avoid repeated reallocations and copies of object's string value).

**Tcl\_AppendObjToObj** is similar to **Tcl\_AppendToObj**, but it appends the string or Unicode value (whichever exists and is best suited to be appended to *objPtr*) of *appendObjPtr* to *objPtr*.

**Tcl\_AppendStringsToObj** is similar to **Tcl\_AppendToObj** except that it can be passed more than one value to append and each value must be a null-terminated string (i.e. none of the values may contain internal null characters).  Any number of *string* arguments may be provided, but the last argument must be a NULL pointer to indicate the end of the list.

**Tcl\_AppendStringsToObjVA** is the same as **Tcl\_AppendStringsToObj** except that instead of taking a variable number of arguments it takes an argument list.

The **Tcl\_SetObjLength** procedure changes the length of the string value of its *objPtr* argument.  If the *newLength* argument is greater than the space allocated for the object's string, then the string space is reallocated and the old value is copied to the new space; the bytes between the old length of the string and the new length may have arbitrary values. If the *newLength* argument is less than the current length of the object's string, with *objPtr-\>length* is reduced without reallocating the string space; the original allocated size for the string is recorded in the object, so that the string length can be enlarged in a subsequent call to **Tcl\_SetObjLength** without reallocating storage.  In all cases **Tcl\_SetObjLength** leaves a null character at *objPtr-\>bytes\[newLength\]*.

The **Tcl\_ConcatObj** function returns a new string object whose value is the space-separated concatenation of the string representations of all of the objects in the *objv* array. **Tcl\_ConcatObj** eliminates leading and trailing white space as it copies the string representations of the *objv* array to the result. If an element of the *objv* array consists of nothing but white space, then that object is ignored entirely. This white-space removal was added to make the output of the **concat** command cleaner-looking. **Tcl\_ConcatObj** returns a pointer to a newly-created object whose ref count is zero.

## SEE ALSO

Tcl\_NewObj, Tcl\_IncrRefCount, Tcl\_DecrRefCount

## KEYWORDS

append, internal representation, object, object type, string object, string type, string representation, concat, concatenate, unicode