底层如何操作字符串

char *strcpy(char *strDes, const char *strSrc) { assert((strDes != NULL) && (strSrc != NULL)); char *address = strDes; while ((*strDes ++ = *strSrc ++) != '\0') NULL; return address; } char *strchr_(char *str, int c) { assert(str != NULL); while ((*str != (char) c) && (*str != '\0')) str ++; if (*str != '\0') return str; return NULL; } char *strchr(const char *str, int c) { assert(str != NULL); for (; *str != (char) c; ++ str) if (*str == '\0') return NULL; return (char *) str; } int strcmp(const char *s, const char *t) { assert(s != NULL && t != NULL); while (*s && *t && *s == *t) { ++ s; ++ t; } return (*s - *t); } char *strcat(char *strDes, const char *strSrc) { assert((strDes != NULL) && (strSrc != NULL)); char *address = strDes; while (*strDes != '\0') ++ strDes; while ((*strDes ++ = *strSrc ++) != '\0') NULL; return address; } int strlen(const char *str) { assert(str != NULL); int len = 0; while (*str ++ != '\0') ++ len; return len; } char *strdup(const char *strSrc) { assert(strSrc != NULL); int len = 0; while (*strSrc ++ != '\0') ++ len; char *strDes = (char *) malloc (len + 1); while ((*strDes ++ = *strSrc ++) != '\0') NULL; return strDes; } char *strstr(const char *strSrc, const char *str) { assert(strSrc != NULL && str != NULL); const char *s = strSrc; const char *t = str; for (; *t != '\0'; ++ strSrc) { for (s = strSrc, t = str; *t != '\0' && *s == *t; ++s, ++t) NULL; if (*t == '\0') return (char *) strSrc; } return NULL; } char *strncpy(char *strDes, const char *strSrc, int count) { assert(strDes != NULL && strSrc != NULL); char *address = strDes; while (count -- && *strSrc != '\0') *strDes ++ = *strSrc ++; return address; } char *strncat(char *strDes, const char *strSrc, int count) { assert((strDes != NULL) && (strSrc != NULL)); char *address = strDes; while (*strDes != '\0') ++ strDes; while (count -- && *strSrc != '\0' ) *strDes ++ = *strSrc ++; *strDes = '\0'; return address; } int strncmp(const char *s, const char *t, int count) { assert((s != NULL) && (t != NULL)); while (*s && *t && *s == *t && count --) { ++ s; ++ t; } return (*s - *t); } char *strpbrk(const char *strSrc, const char *str) { assert((strSrc != NULL) && (str != NULL)); const char *s; while (*strSrc != '\0') { s = str; while (*s != '\0') { if (*strSrc == *s) return (char *) strSrc; ++ s; } ++ strSrc; } return NULL; } int strcspn(const char *strSrc, const char *str) { assert((strSrc != NULL) && (str != NULL)); const char *s; const char *t = strSrc; while (*t != '\0') { s = str; while (*s != '\0') { if (*t == *s) return t - strSrc; ++ s; } ++ t; } return 0; } int strspn(const char *strSrc, const char *str) { assert((strSrc != NULL) && (str != NULL)); const char *s; const char *t = strSrc; while (*t != '\0') { s = str; while (*s != '\0') { if (*t == *s) break; ++ s; } if (*s == '\0') return t - strSrc; ++ t; } return 0; } char *strrchr(const char *str, int c) { assert(str != NULL); const char *s = str; while (*s != '\0') ++ s; for (-- s; *s != (char) c; -- s) if (s == str) return NULL; return (char *) s; } char* strrev(char *str) { assert(str != NULL); char *s = str, *t = str, c; while (*t != '\0') ++ t; for (-- t; s < t; ++ s, -- t) { c = *s; *s = *t; *t = c; } return str; } char *strnset(char *str, int c, int count) { assert(str != NULL); char *s = str; for (; *s != '\0' && s - str < count; ++ s) *s = (char) c; return str; } char *strset(char *str, int c) { assert(str != NULL); char *s = str; for (; *s != '\0'; ++ s) *s = (char) c; return str; } char *strtok(char *strToken, const char *str) { assert(strToken != NULL && str != NULL); char *s = strToken; const char *t = str; while (*s != '\0') { t = str; while (*t != '\0') { if (*s == *t) { *(strToken + (s - strToken)) = '\0'; return strToken; } ++ t; } ++ s; } return NULL; } char *strupr(char *str) { assert(str != NULL); char *s = str; while (*s != '\0') { if (*s >= 'a' && *s <= 'z') *s -= 0x20; s ++; } return str; } char *strlwr(char *str) { assert(str != NULL); char *s = str; while (*s != '\0') { if (*s >= 'A' && *s <= 'Z') *s += 0x20; s ++; } return str; } void *memcpy(void *dest, const void *src, int count) { assert((dest != NULL) && (src != NULL)); void *address = dest; while (count --) { *(char *) dest = *(char *) src; dest = (char *) dest + 1; src = (char *) src + 1; } return address; } void *memccpy(void *dest, const void *src, int c, unsigned int count) { assert((dest != NULL) && (src != NULL)); while (count --) { *(char *) dest = *(char *) src; if (* (char *) src == (char) c) return ((char *)dest + 1); dest = (char *) dest + 1; src = (char *) src + 1; } return NULL; } void *memchr(const void *buf, int c, int count) { assert(buf != NULL); while (count --) { if (*(char *) buf == c) return (void *) buf; buf = (char *) buf + 1; } return NULL; } int memcmp(const void *s, const void *t, int count) { assert((s != NULL) && (t != NULL)); while (*(char *) s && *(char *) t && *(char *) s == *(char *) t && count --) { s = (char *) s + 1; t = (char *) t + 1; } return (*(char *) s - *(char *) t); } void *memmove(void *dest, const void *src, int count) { assert(dest != NULL && src != NULL); void *address = dest; while (count --) { *(char *) dest = *(char *) src; dest = (char *) dest + 1; src = (const char *)src + 1; } return address; } void *memset(void *str, int c, int count) { assert(str != NULL); void *s = str; while (count --) { *(char *) s = (char) c; s = (char *) s + 1; } return str; }