Getting filenames from the command line

Next, copy the program into open_close_argv.c and modify it to match the following program:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/errno.h>// for errno

void usage( char* cmd ){
fprintf( stderr , "usage: %s inputFileName outputFileName\n" , 
           cmd );
exit( 0 );
}

int main( int argc, char *argv[] )  {
FILE* inputFile= NULL;
FILE* outputFile = NULL;

if( argc != 3 ) usage( argv[0] );
if( NULL == ( inputFile = fopen( argv[1] , "r") ) ){
fprintf( stderr, "input file: %s: %s\n", 
             argv[1], strerror(errno));
exit( 1 );
}
if( NULL == ( outputFile = fopen( argv[2] , "w" ) ) ){
fprintf( stderr, "output file: %s: %s\n", 
             argv[2], strerror(errno));
exit( 1 );
}

fprintf( stderr , "%s opened for reading.\n" , argv[1] );
fprintf( stderr , "%s opened for writing.\n" , argv[2] );
fprintf( stderr , "Do work...