## Tcl8.6.0/Tk8.6.0 Documentation > Tcl C API, version 8.6.0 > Alloc

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  NAME
    Tcl_Alloc, Tcl_Free, Tcl_Realloc, Tcl_AttemptAlloc, Tcl_AttemptRealloc, ckalloc, ckfree, ckrealloc, attemptckalloc, attemptckrealloc — allocate or free heap memory
  SYNOPSIS
    #include <tcl8.6/tcl.h>
    char *
    Tcl_Alloc(size)
    void
    Tcl_Free(ptr)
    char *
    Tcl_Realloc(ptr, size)
    char *
    Tcl_AttemptAlloc(size)
    char *
    Tcl_AttemptRealloc(ptr, size)
    char *
    ckalloc(size)
    void
    ckfree(ptr)
    char *
    ckrealloc(ptr, size)
    char *
    attemptckalloc(size)
    char *
    attemptckrealloc(ptr, size)
  ARGUMENTS
  DESCRIPTION
  KEYWORDS

### NAME

Tcl_Alloc, Tcl_Free, Tcl_Realloc, Tcl_AttemptAlloc, Tcl_AttemptRealloc, ckalloc, ckfree, ckrealloc, attemptckalloc, attemptckrealloc — allocate or free heap memory

### SYNOPSIS

#include <tcl8.6/tcl.h>
char *
Tcl_Alloc(size)
void
Tcl_Free(ptr)
char *
Tcl_Realloc(ptr, size)
char *
Tcl_AttemptAlloc(size)
char *
Tcl_AttemptRealloc(ptr, size)
char *
ckalloc(size)
void
ckfree(ptr)
char *
ckrealloc(ptr, size)
char *
attemptckalloc(size)
char *
attemptckrealloc(ptr, size)

### ARGUMENTS

unsigned int size (in)
  Size in bytes of the memory block to allocate.

char *ptr (in)
  Pointer to memory block to free or realloc.

### DESCRIPTION

These procedures provide a platform and compiler independent interface for memory allocation. Programs that need to transfer ownership of memory blocks between Tcl and other modules should use these routines rather than the native malloc() and free() routines provided by the C run-time library.

Tcl_Alloc returns a pointer to a block of at least size bytes suitably aligned for any use.

Tcl_Free makes the space referred to by ptr available for further allocation.

Tcl_Realloc changes the size of the block pointed to by ptr to size bytes and returns a pointer to the new block. The contents will be unchanged up to the lesser of the new and old sizes. The returned location may be different from ptr. If ptr is NULL, this is equivalent to calling Tcl_Alloc with just the size argument.

Tcl_AttemptAlloc and Tcl_AttemptRealloc are identical in function to Tcl_Alloc and Tcl_Realloc, except that Tcl_AttemptAlloc and Tcl_AttemptRealloc will not cause the Tcl interpreter to panic if the memory allocation fails. If the allocation fails, these functions will return NULL. Note that on some platforms, but not all, attempting to allocate a zero-sized block of memory will also cause these functions to return NULL.

The procedures ckalloc, ckfree, ckrealloc, attemptckalloc, and attemptckrealloc are implemented as macros. Normally, they are synonyms for the corresponding procedures documented on this page. When Tcl and all modules calling Tcl are compiled with TCL_MEM_DEBUG defined, however, these macros are redefined to be special debugging versions of these procedures. To support Tcl's memory debugging within a module, use the macros rather than direct calls to Tcl_Alloc, etc.

### KEYWORDS

alloc, allocation, free, malloc, memory, realloc, TCL_MEM_DEBUG
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