pointer pointer pointer

void GetMemory( char *p ){
    p = (char *) malloc( 100 );
}

void Test( void ) {
    char *str = NULL;
    GetMemory( str ); 
    strcpy( str, "hello world" );
    printf( str );
}

在GetMemory中， p是local variable, 所以GetMemory( str )後，str仍然是NULL.
應改為

void GetMemory( char **p ){
    p = (char *) malloc( 100 );
}

void Test( void ) {
    char *str = NULL;
    GetMemory( &str ); 
    strcpy( str, "hello world" );
    printf( str );
}