函数strcpy、strcat和strcmp实现源码 _用函数封装的情况下,完成stract和strcpy功能-优快云博客

前两天在codeproject挖坟时找到的......

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/************************************************************************

*char *strcpy(dst, src) - copy one string over another

*

*Purpose:

* Copies the string src into the spot specified by

* dest; assumes enough room.

*

*Entry:

* char * dst - string over which "src" is to be copied

* const char * src - string to be copied over "dst"

*

*Exit:

* The address of "dst"

*

*Exceptions:
************************************************************************/
char* strcpy(char * dst, const char * src)
{
    char * cp = dst;
    while( *cp++ = *src++ )
        ;                           /* Copy src over dst */
    return( dst );
}

/************************************************************************

*char *strcat(dst, src) - concatenate (append) one string to another

*

*Purpose:

* Concatenates src onto the end of dest. Assumes enough

* space in dest.

*

*Entry:

* char *dst - string to which "src" is to be appended

* const char *src - string to be appended to the end of "dst"

*

*Exit:

* The address of "dst"

*

*Exceptions:

*
************************************************************************/
char* strcat ( char * dst , const char * src )
{
    char * cp = dst;
    while( *cp )
        cp++;                       /* find end of dst */
    while( *cp++ = *src++ ) ;       /* Copy src to end of dst */
    return( dst );                  /* return dst */
}

/************************************************************************

*strcmp - compare two strings, returning less than, equal to, or greater than

*

*Purpose:

* STRCMP compares two strings and returns an integer

* to indicate whether the first is less than the second, the two are

* equal, or whether the first is greater than the second.

*

* Comparison is done byte by byte on an UNSIGNED basis, which is to

* say that Null (0) is less than any other character (1-255).

*

*Entry:

* const char * src - string for left-hand side of comparison

* const char * dst - string for right-hand side of comparison

*

*Exit:

* returns -1 if src < dst

* returns 0 if src == dst

* returns +1 if src > dst

*

*Exceptions:

*
************************************************************************/
int strcmp ( const char* src, const char* dst )
{
    int ret = 0 ;
    while( !(ret = *(unsigned char *)src - *(unsigned char *)dst) && *dst)
        ++src, ++dst;
    if ( ret < 0 )
        ret = -1 ;
    else if ( ret > 0 )
        ret = 1 ;
    return( ret );
}