模拟实现C库函数strcpy,strcat,strstr,strchr,strcmp,memcpy,memmove

1、模拟实现strcpy

char *my_strcpy( char *dest, const char *str) { assert(dest != NULL); assert(str != NULL); while (*dest++=*str++) { ; } return dest; } int main() { char p[20]; char *p1 = "world"; my_strcpy(p, p1); printf("%s\n", p); system("pause"); return 0; } 2、模拟实现strcat

char* my_strcat(char*dest, const char* str) { assert(dest != NULL); assert(str != NULL); char *ret = dest; while (*dest) { dest++; } while (*str) { *dest++ = *str++; } return ret; } int main() { char p[20] = "hello "; my_strcat(p, "world"); printf("%s", p); system("pause"); return 0; }

3、模拟实现strstr

char* my_strstr(const char *dest, const char*str) { assert(dest != NULL); assert(str != NULL); char *ret = (char*)dest; char *cur = (char*)str; while (*cur) { if ((*ret) && (*cur) && (*ret++ = *cur++)) { return cur; } cur++; } return NULL; } int main() { char p[] = "abcdefd"; char* p1 = "defr"; char* ret = NULL; ret= strstr(p, p1); if (ret == NULL) { printf("no"); } else { printf("%s", ret); } system("pause"); } 4、模拟实现strchr

char* my_strchr(const char*dest, int x) { assert(dest != NULL); char*ret = (char*)dest; while (*ret) { if ((*ret) && (*ret == x)) { return ret; } ret++; } return NULL; } int main() { char p[] = "abcdefg"; char*ret=my_strchr(p, 'f'); if (ret == NULL) { printf("no\n"); } else { printf("%s", ret); } system("pause"); }5、模拟实现strcmp

int my_strcmp(const char*str1, const char*str2) { assert(str1 != NULL); assert(str2 != NULL); while (*str1==*str2) { if (*str1 == '\0') { return 0; } *str1++; *str2++; } if (*str1 > *str2) { return 1; } else if (*str1 < *str2) { return -1; } } int main() { char p1[] = "dccbcc"; char p2[] = "dccccc"; int ret = my_strcmp(p1, p2); printf("%d\n", ret); system("pause"); }

6、模拟实现memcpy

void*my_memcpy(void*dest, const void*str, size_t sz) { assert(dest != NULL); assert(str != NULL); char* ret = (char*)str; char* cur = (char*)dest; while (sz--) { *cur++ = *ret++; } return dest; } int main() { char p1[20] = { 0 }; char* p2 = "world"; my_memcpy(p1, p2, 4); printf("%s\n", p1); system("pause"); return 0; } 7、模拟实现memmove

void* my_memmove(void*dest, const void*str, size_t len) { assert(dest != NULL); assert(str != NULL); char *pdest = (char*)dest; char* pstr = (char*)str; if ((pstr < pdest) && (pdest < pstr + len)) { while (len--) { *(pdest+len) = *(pstr+len); } } else { while (len--) { *pdest++ = *pstr++; } } return dest; } int main() { char p[] = "abcdefgh"; my_memmove(p, p+2, 4); printf("%s", p); system("pause"); return 0; }