Prototype

Declared in string.h

The C89/C99 prototype is:

void *memchr(const void *s, int c, size_t n);

Description

The memchr() function locates the first occurrence of c (converted to an unsigned char) in the initial n characters (each interpreted as unsigned char) of the object pointed to by s.

Return value

The memchr() function returns a pointer to the located character, or a null pointer if the character does not occur in the object.

Implementation

In standard C, this can be implemented as:

#include <stddef.h>
void *memchr(const void *s, int c, size_t n)
{
    unsigned char *p = (unsigned char*)s;
    while( n-- )
        if( *p != (unsigned char)c )
            p++;
        else
            return p;
    return 0;
}

Compilable unit, portable C90 in implementation namespace; public domain; past reviewers: none; current reviews: GabrielRavier with this code (structured testing);

Test harness

#include <stdio.h>
void test_memchr(void)
{
	char *s1 = "";
	char *s2 = "abcdefabcdef";
	char *s3 = "11111111111111111111";

	printf("Testing memchr():\nTest1...");
	if (memchr(s1, 'x', 0) == NULL)
		printf("passed.");
	else	printf("FAILED.");
	printf("\nTest2...");
	if (memchr(s2, 'y', 0) == NULL)
		printf("passed.");
	else	printf("FAILED.");
	printf("\nTest3...");
	if ((char *)memchr(s2, 'a', 1) - s2 == 0)
		printf("passed.");
	else	printf("FAILED.");
	printf("\nTest4...");
	if (memchr(s2, 'd', 2)  == NULL)
		printf("passed.");
	else	printf("FAILED.");
	printf("\nTest5...");
	if ((char *)memchr(s2, 'd', 12)  - s2 == 3)
		printf("passed.");
	else	printf("FAILED.");
	printf("\nTest6...");
	if ((char *)memchr(s2, 'f', 12)  - s2 == 5)
		printf("passed.");
	else	printf("FAILED.");
	printf("\nTest7...");
	if ((char *)memchr(s3, '1', 20)  - s3 == 0)
		printf("passed.");
	else	printf("FAILED.");
	putchar('\n');
}

int main(void)
{
	test_memchr();
	return 0;
}

References

The C Standard, 7.21.5.1 (C99 numbering)