字符串处理函数C语言实现（一）

包含以下函数： //字符串查找将在下篇文章详细说明

size_t lm_strlen(const char *str);
size_t lm_strlen2(const char *str);
char * lm_strcpy(char *dest, const char *src);
char * lm_strncpy(char *dest, const char *src, size_t n);
char * lm_strncpy2(char *dest, const char *src, size_t n);
char * lm_strcat (char *dest, const char *src);
char * lm_strcat2 (char *dest, const char *src);
char * lm_strncat (char *dest, const char *src, size_t n);
char * lm_strncat2 (char *dest, const char *src, size_t n);
int lm_strcmp(const char *s1, const char *s2);
int lm_strncmp(const char *s1, const char *s2, size_t n);

//注：有些函数名字后面有2的表示第二钟方法
size_t lm_strlen(const char *str){
 int len;
 for(len = 0; '/0' != *str++; )
  ++len;
 return len;
}

size_t lm_strlen2(const char *str){
 const char *psz = str;
 while(*psz++)
  ;
 return (psz-str-1);
}

/* 从src复制源字符串到dest，包括结束符'/0',如果dest数组容量不够，继续覆盖dest数组后面的内存

*/
char * lm_strcpy(char *dest, const char *src){
  //if( (!dest)||(!src) ) return NULL;  //通常为了保持高效不加判断
  char *save = dest;
  while(*dest++ = *src++)
   ;
  return save;
}

char * lm_strncpy(char *dest, const char *src, size_t n){
  char *start = dest;
  char *end = dest + n;

  while ((start < end) && (*start++ = *src++))
    ;

  return (dest);
}

char * lm_strncpy2(char *dest, const char *src, size_t n){
  if (n > 0) {
    char *d = dest;
    const char *s = src;

    do {
      if ((*d++ = *s++) == 0){
        //如果n大于字符串src的长度，dest多余部分清0
       while (--n != 0)
         *d++ = 0;
       break;
      }
    } while (--n != 0);
  }
  return dest;
}

char * lm_strcat (char *dest, const char *src){
  //if( (!dest ) return NULL;
  //if( !src ) return dest;
  lm_strcpy (dest + lm_strlen (dest), src);
  return dest;
}

char * lm_strcat2 (char *dest, const char *src){
    char *save;
    //if( (!dest ) return NULL;
    //if( !src ) return dest;
    for(save = dest; *dest; dest++ )
  ;

    for( ; (*dest = *src); dest++, src++ )
  ;
    return save;
}

char * lm_strncat (char *dest, const char *src, size_t n){
  //if( (!dest ) return NULL;
  //if( !src ) return dest;
  lm_strncpy (dest + lm_strlen (dest), src, n);
  return dest;
}

char * lm_strncat2 (char *dest, const char *src, size_t n){
    char *save;
    //if( (!dest ) return NULL;
    //if( !src ) return dest;
    for(save = dest; *dest; dest++ )
  ;

    for( ; (n>0)&&(*dest = *src); dest++, src++, n--)
  ;
    return save;
}

int lm_strcmp(const char *s1, const char *s2){
  while (*s1 != '/0' && *s1 == *s2) {
 s1++;
 s2++;
  }
  return(*s1 - *s2);
}

int lm_strncmp(const char *s1, const char *s2, size_t n){
  while (n-- > 0 && *s1 != '/0' && *s1 == *s2){
    s1++;
   s2++;
  }
  return(*s1 - *s2);
}