alloca
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Note: This feature is available only for the classic bcc32 compiler, not for the modern Clang-enhanced compiler.
Header File
malloc.h
Prototype
void *alloca(size_t size);
Description
Allocates temporary stack space.
alloca allocates size bytes on the stack; the allocated space is automatically freed up when the calling function exits.
The use of alloca is not encouraged. In the try-block of a C++ program the alloca function should never be used. If an exception is thrown, any values placed on the stack by alloca will be corrupted.
Return Value
If enough stack space is available, alloca returns a pointer to the allocated stack area. Otherwise, it returns NULL.
Portability
POSIX | ANSI C | ANSI C++ | Win32 | Win64 | macOS | |
---|---|---|---|---|---|---|
alloca | + |
Example
#include <malloc.h>
#include <stdio.h>
#include <stdlib.h>
void test(int a) {
char *newstack;
int len = a;
char dummy[1];
dummy[0] = 0; /* force good stack frame */
printf("SP before calling alloca(0x%X) = 0x%X\n", len, _SP);
newstack = (char *) alloca(len);
printf("SP after calling alloca = 0x%X\n", _SP);
if (newstack)
printf("Alloca(0x%X) returned %p\n", len, newstack);
else
printf("Alloca(0x%X) failed\n", len);
}
void main() {
test(256);
test(16384);
}