string.c

#include <stdio.h>
#include <stdlib.h>

int my_strlen(char *str);
void my_strcpy(char *source, char *target);
int my_strstr(char *haystack, char *needle);

int main()
{
	char *wut = "123wuwut456\0";
	int len = my_strlen(wut);
	printf("Length: %i\n", len);
	
	char *needle = "wut\0";
	printf("Offset: %d\n", my_strstr(wut, needle));

	char *out = (char*)calloc(len, sizeof(char*));
	my_strcpy(wut, out);
	printf("Copy out: %s\n", out);

	return 0;
}

int my_strlen(char *str)
{
	char *s;
	for (s = str; *s; ++s);
	return (s - str);
}

void my_strcpy(char *source, char *target)
{
	char* _target = target;
	for (char *s = source; *s; ++s, ++_target)
		*_target = *s;
}

int my_strstr(char *haystack, char *needle)
{
	size_t offset = -1;

	char *_haystack;
	char *_needle = needle;
	for (_haystack = haystack; *_haystack, *_needle; ++_haystack)
	{
		if (*_haystack == *_needle && offset == -1)
			offset = _haystack;

		if (offset != -1 && *_needle)
		{
			if (*_haystack != *_needle)
			{
				_haystack = offset + 1;
				_needle = needle;
				offset = -1;
			}
			else
			++_needle;
		}
	}
	if (offset != -1)
		return offset - (size_t)haystack;
	return -1;
}