16进制串hex与ASCII字符串相互转换

char *chstohex ( char* chs )
{
char hex[16] = { '0', '1', '2', '3', '4', '5', '6', \
'7', '8','9', 'A', 'B', 'C', 'D', 'E', 'F'
};

int len = strlen ( chs );
char* ascii = NULL ;
ascii = (char*)calloc ( len * 3 + 1, sizeof(char) );            // calloc ascii

int i = 0;
while( i < len )
{
ascii[i*2] = hex[(int)( (char)chs[i] / 16 )] ;
ascii[i*2 + 1] = hex[(int)( (char)chs[i] % 16 )] ;
++i;
}

return ascii;                    // ascii 返回之前未释放
}
// 函数输入16进制字符串，输出对应的字符串
char *hextochs ( char* ascii )
{
int len = strlen ( ascii ) ;
if( len%2 != 0 )
return NULL ;
char *chs = NULL ;
chs = (char*)calloc( len / 2 + 1, sizeof(char) );                // calloc chs

int  i = 0 ;
char ch[2] = {0};
while( i < len )
{
ch[0] = ( (int)ascii[i] > 64 ) ? ( ascii[i]%16 + 9 ) : ascii[i]%16 ;
ch[1] = ( (int)ascii[i + 1] > 64 ) ? ( ascii[i + 1]%16 + 9 ) : ascii[i + 1]%16 ;

chs[i/2] = (char)( ch[0]*16 + ch[1] );
i += 2;
}

return chs ;            // chs 返回前未释放
}