常用辅助函数集合

1. strncpy源码

char *strncpy(char *dest, const char *src, size_t count)
{
    char *tmp = dest;
    while (count) {
        if ((*tmp = *src) != 0)
            src++;
        tmp++;
        count--;
    }
    return dest;
}

返回dest指针的目的是链式表达式

2. strlen源码

(1)

int myStrlen(const char *str)

{

    assert(str != NULL); 

    int len = 0; 
    while ((*str++) != '\0') len++; 
    return len; 
}

(2)不带变量，递归方式

int myStrlen(const char *str)
{
    assert(str != NULL); 
    return *str == '\0' ? 0 : (1+myStrlen(++str)); 
}

3. strcmp源码

int myStrcmp(const char *str1, const char *str2)
{
    assert(str1 != NULL && str2 != NULL); 
    int ret = 0; 
    while (!(ret=*(unsigned char *)str1 - *(unsigned char *)str2) && *str1)
    {
        str1++; 
        str2++; 
    }
    if (ret < 0) ret = -1; 
    else if (ret > 0) ret = 1; 
    return ret; 
}

4. strcat源码

char *myStrcat(char *strDest, const char *strSrc)
{
    char *address = strDest; 
    assert(strDest != NULL && strSrc != NULL); 
    while (*strDest) strDest++; 
    while (*strDest++ = *strSrc++) ; 
    return address; 
}

5. strcpy源码

char *strcpy(char *strDest, const char *strSrc)
{ 
    assert(strDest != NULL && strSrc != NULL); 
    char *address = strDest; 
    while ((*strDest++ = *strSrc++) != '\0') ; 
    return address; 
}

6.