CODEWITHSUNDEEP
clinuxfilesymlink
Mike
Mike

Reputation: 131

program that checks if the files match

My program check if two files (with a different path / name) match or not. The hard and symbolic links between the files are followed to determine it.

How can I modify the program to see what happens if the files I want to compare are device files? Or directories? Both seem valid uses. Also checking the device

#include <unistd.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>

void printUsage()
{
    printf("Use: ./leg <name_file1> <name_file2>.\n");
}

int createStat(const char *file, struct stat *fileStat)
{
    if (stat(file, fileStat) < 0)
    {
        fprintf(stderr,"Error! File %s does not exist.\n", file);
        return 0;
    }
    return 1;
}

int main(int argc, char **argv)
{
    if (argc < 3)
    {    
        printf("Insufficient number of parameters.\n");
        printUsage();
        return -1;
    }

    struct stat fileStat1;
    struct stat fileStat2;
    if (createStat(argv[1], &fileStat1) == 0)
    {
        return -1;
    }
    if (createStat(argv[2], &fileStat2) == 0)
    {
        return -1;
    }
    if (S_ISREG(fileStat1.st_mode) && S_ISREG(fileStat2.st_mode)) {
        if ((fileStat1.st_dev == fileStat2.st_dev) && (fileStat1.st_ino == fileStat2.st_ino)) {
            printf("Files '%s' and '%s' coincide.\n", argv[1], argv[2]);
        } else
            printf("Files '%s' and '%s' do not match.\n", argv[1], argv[2]);
    } else
        fprintf(stderr,"'%s' and '%s' there are no files.\n", argv[1], argv[2]);

    return 0;
}

Upvotes: 0

Views: 122

Answers (1)

chqrlie
chqrlie

Reputation: 144550

For regular files and directories, comparing the st_dev and st_ino fields is sufficient.

For paths representing character or block devices, comparing the st_dev and st_ino fields will tell you if they are the same file, ie: different paths to the same directory entry, including symbolic link indirections. Comparing the st_rdev fields will tell if they represent the same device, which is also useful but a different thing.

Also note that fprintf(stderr,"Error! File %s does not exist.\n", file); may produce a misleading message: access failure may be caused by other reasons. It is simple and efficient to produce the correct message this way:

#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

int createStat(const char *file, struct stat *fileStat) {
    if (stat(file, fileStat) < 0) {
        fprintf(stderr, "Cannot stat file %s: %s\n", file, strerror(errno));
        return 0;
    }
    return 1;
}

Upvotes: 2

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