1. strncmp
int my_strncmp(const char *s1, const char *s2, size_t n) {
assert(s1 && s2);
while (--n && *s1 && *s1 == *s2) { s1++; s2++; }
return *s1 - *s2;
}
2. strncat
char *my_strncat(char *dst, const char *src, size_t n) {
assert(dst && src);
char *ret = dst;
while (*dst) dst++;
while (n-- && *src) *dst++ = *src++;
*dst = '\0';
return ret;
}
3. memset
void *my_memset(void *s, int ch, size_t n) {
assert(s);
void *ret = s;
while (n--) *(char*)s++ = (char)ch;
return ret;
}
4. memcmp
int my_memcmp(const void *s1, const void *s2, size_t n) {
const char *a = s1, *b = s2;
while (--n && *a && *a == *b) { a++; b++; }
return *a - *b;
}
測試主程序
int main() {
char a[]="abcdef", b[]="abcdeg";
printf("strncmp: %d\n", my_strncmp(a,b,3)); // 0
char buf[20]="hi "; my_strncat(buf,"there",3); printf("strncat: %s\n",buf); // hi the
char c[10]; my_memset(c,'X',5); c[5]='\0'; printf("memset: %s\n",c); // XXXXX
printf("memcmp: %d\n", my_memcmp(a,b,6)); // 負值
return 0;
}
