Tcl_NewByteArrayObj man page

Tcl_NewByteArrayObj, Tcl_SetByteArrayObj, Tcl_GetByteArrayFromObj, Tcl_SetByteArrayLength — manipulate Tcl values as a arrays of bytes


#include <tcl.h>

Tcl_Obj *
Tcl_NewByteArrayObj(bytes, length)

Tcl_SetByteArrayObj(objPtr, bytes, length)

unsigned char *
Tcl_GetByteArrayFromObj(objPtr, lengthPtr)

unsigned char *
Tcl_SetByteArrayLength(objPtr, length)


const unsigned char *bytes (in)
The array of bytes used to initialize or set a byte-array value. May be NULL even if length is non-zero.
int length (in)
The length of the array of bytes. It must be >= 0.
Tcl_Obj *objPtr (in/out)
For Tcl_SetByteArrayObj, this points to the value to be converted to byte-array type. For Tcl_GetByteArrayFromObj and Tcl_SetByteArrayLength, this points to the value from which to get the byte-array value; if objPtr does not already point to a byte-array value, it will be converted to one.
int *lengthPtr (out)
If non-NULL, filled with the length of the array of bytes in the value.


These procedures are used to create, modify, and read Tcl byte-array values from C code. Byte-array values are typically used to hold the results of binary IO operations or data structures created with the binary command. In Tcl, an array of bytes is not equivalent to a string. Conceptually, a string is an array of Unicode characters, while a byte-array is an array of 8-bit quantities with no implicit meaning. Accessor functions are provided to get the string representation of a byte-array or to convert an arbitrary value to a byte-array. Obtaining the string representation of a byte-array value (by calling Tcl_GetStringFromObj) produces a properly formed UTF-8 sequence with a one-to-one mapping between the bytes in the internal representation and the UTF-8 characters in the string representation.

Tcl_NewByteArrayObj and Tcl_SetByteArrayObj will create a new value of byte-array type or modify an existing value to have a byte-array type. Both of these procedures set the value's type to be byte-array and set the value's internal representation to a copy of the array of bytes given by bytes. Tcl_NewByteArrayObj returns a pointer to a newly allocated value with a reference count of zero. Tcl_SetByteArrayObj invalidates any old string representation and, if the value is not already a byte-array value, frees any old internal representation. If bytes is NULL then the new byte array contains arbitrary values.

Tcl_GetByteArrayFromObj converts a Tcl value to byte-array type and returns a pointer to the value's new internal representation as an array of bytes. The length of this array is stored in lengthPtr if lengthPtr is non-NULL. The storage for the array of bytes is owned by the value and should not be freed. The contents of the array may be modified by the caller only if the value is not shared and the caller invalidates the string representation.

Tcl_SetByteArrayLength converts the Tcl value to byte-array type and changes the length of the value's internal representation as an array of bytes. If length is greater than the space currently allocated for the array, the array is reallocated to the new length; the newly allocated bytes at the end of the array have arbitrary values. If length is less than the space currently allocated for the array, the length of array is reduced to the new length. The return value is a pointer to the value's new array of bytes.

See Also

Tcl_GetStringFromObj, Tcl_NewObj, Tcl_IncrRefCount, Tcl_DecrRefCount


value, binary data, byte array, utf, unicode, internationalization

Referenced By


Tcl_GetByteArrayFromObj(3), Tcl_SetByteArrayLength(3) and Tcl_SetByteArrayObj(3) are aliases of Tcl_NewByteArrayObj(3).

8.1 Tcl Tcl Library Procedures