C语言常用库函数实现

对于C 语言来说远着许多的函数需要记住，因此是十分考验技巧的'语言，但是也是学习编程的入门知识，下面是小编为大家搜集整理出来的有关于C常用库函数实现，希望可以帮助到大家!

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123 C常用库函数实现// ---------- strlen -------------int strlen(char *t){int length = 0;if(t == NULL)return -1;while (*t != '') {t++;length++;}return length;}size_t strlen(const char *s){const char *sc;for (sc = s; *sc != ''; ++sc);return sc - s;}// ---------- trim -------------void ltrim ( char *s ){char *p;p = s;while ( *p == ' ' || *p == ' ' ) {p++;}strcpy ( s,p );}void rtrim ( char *s ){int i;i = strlen ( s )-1;while ( ( s[i] == ' ' || s[i] == ' ' ) && i >= 0 ) {i--;};s[i+1] = '';}void trim ( char *s ){ltrim ( s );rtrim ( s );}// ---------- strcpy -------------char *strcpy(char *dest, const char *src){char *tmp = dest;while ((*dest++ = *src++) != '');return tmp;}// ---------- strcat -------------char *strcat(char *dest, const char *src){char *tmp = dest;while (*dest)dest++;while ((*dest++ = *src++) != '');return tmp;}// ---------- strstr -------------char *strstr(const char *s1, const char *s2){int l1, l2;l2 = strlen(s2);if (!l2)return (char *)s1;l1 = strlen(s1);while (l1 >= l2) {l1--;if (!memcmp(s1, s2, l2))return (char *)s1;s1++;}return NULL;}// ---------- memcmp -------------int memcmp(char *cs, char *ct, size_t count){char *su1, *su2;int res = 0;for (su1 = cs, su2 = ct; 0 < count; ++su1, ++su2, count--)if ((res = *su1 - *su2) != 0)break;return res;}// ---------- strcmp -------------int strcmp(const char *cs, const char *ct){unsigned char c1, c2;while (1) {c1 = *cs++;c2 = *ct++;if (c1 != c2)return c1 < c2 ? -1 : 1;if (!c1)break;}return 0;}

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