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/* COPY1.C illustrates low-level file I/O and dynamic memory allocation
 * functions including:
 *      open            close
 *      read            write           eof
 *      malloc          free            _memmax
 *
 * Also the global variable:
 *      errno
 *
 * See COPY2.C for another version of the copyfile function and
 * HEAPBASE.C for an example of based heap management.
 */
 
#include <io.h>
#include <conio.h>
#include <stdio.h>
#include <fcntl.h>          /* O_ constant definitions */
#include <sys\types.h>
#include <sys\stat.h>       /* S_ constant definitions */
#include <malloc.h>
#include <errno.h>
 
int copyfile( char *source, char *destin );     /* Prototype */
 
void main( int argc, char *argv[] )
{
    if( argc == 3 )
        if( copyfile( argv[1], argv[2] ) )
            printf( "Copy failed\n" );
        else
            printf( "Copy successful\n" );
    else
        printf( "  SYNTAX: COPY1 <source> <target>\n" );
}
 
/* Copies one file to another (both specified by path). Dynamically
 * allocates memory for the file buffer. Prompts before overwriting
 * existing file. Returns 0 if successful, otherwise an error number.
 */
int copyfile( char *source, char *target )
{
    char *buf;
    int hsource, htarget, ch;
    unsigned count = 0xff00;
 
    /* Open source file and create target, overwriting if necessary. */
    if( (hsource = open( source, O_BINARY | O_RDONLY )) == - 1 )
        return errno;
    htarget = open( target, O_BINARY | O_WRONLY | O_CREAT | O_EXCL,
                            S_IREAD | S_IWRITE );
    if( errno == EEXIST )
    {
        cputs( "Target exists. Overwrite? " );
        ch = getch();
        if( (ch == 'y') || (ch == 'Y') )
            htarget = open( target, O_BINARY | O_WRONLY | O_CREAT | O_TRUNC,
                                    S_IREAD | S_IWRITE );
        printf( "\n" );
    }
    if( htarget == -1 )
        return errno;
 
    if( filelength( hsource ) < count )
        count = (int)filelength( hsource );
 
    /* Dynamically allocate a large file buffer. If there's not enough
     * memory for it, find the largest amount available on the near heap
     * and allocate that. This can't fail, no matter what the memory model.
     */
    if( (buf = (char *)malloc( (size_t)count )) == NULL )
    {
        count = _memmax();
        if( (buf = (char *)malloc( (size_t)count )) == NULL )
            return ENOMEM;
    }
 
    /* Read-write until there's nothing left. */
    while( !eof( hsource ) )
    {
        /* Read and write input. */
        if( (count = read( hsource, buf, count )) == -1 )
            return errno;
        if( (count = write( htarget, buf, count )) == - 1 )
            return errno;
    }
 
    /* Close files and release memory. */
    close( hsource );
    close( htarget );
    free( buf );
    return 0;
}