一个用C实现的URL解码的程序

#include <stdio.h>

/*
* decode encd with URL, the result saved to decd.
* return point to be decoded string.
*/
char *decode( char *encd, char decd[] );

int main( int argc, char *argv[] )
{
    if( argc < 2 )
    return -1;

    char decoded[80];

    decode( argv[1], decoded );
    printf( "%s\n", decoded );

    return 0;
}

char *decode( char *encd, char decd[] )
{
    if( encd == NULL )
        return (char* )0;

    int i, j=0;
    char *cd = encd;
    char p[2];
    unsigned int num;

    for( i = 0; i < strlen( cd ); i++ )
    {
        memset( p, '\0', 2 );
        if( cd[i] != '%' )
        {
            decd[j++] = cd[i];
            continue;
        }
        p[0] = cd[++i];
        p[1] = cd[++i];

        sscanf( p, "%x", &num );
        sprintf(p, "%c", num );
        decd[j++] = p[0];
    }
    decd[j] = '\0';

    return decd;
}