CODEWITHSUNDEEP
clinux
Engine
Engine

Reputation: 5422

getting the oldest file in a directory C

I've asked a similar question about getting the newest file in directory and I've got this answer that I really like :

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

char newest[PATH_MAX];
time_t mtime = 0;

int checkifnewer(const char *path, const struct stat *sb, int typeflag)
{
    if (typeflag == FTW_F && sb->st_mtime > mtime) {
        mtime = sb->st_mtime;
        strncpy(newest, path, PATH_MAX);
    }
    return 0;
}

main()
{
    ftw("./example", checkifnewer, 1); 
    printf("%s\n", newest);
}

I want to use the function to get the oldest file in the directory for that I've tried to change the condition :

 if (typeflag == FTW_F && sb->st_mtime > mtime)

to 

 if (typeflag == FTW_F && sb->st_mtime < mtime)

the program doesn't crash or give any result, any idea how to do this ! for the record thanks to @Mark Plotnick for his answer

Upvotes: 1

Views: 1615

Answers (1)

david.pfx
david.pfx

Reputation: 10868

You need to handle the startup condition. You could try to initialise the value of mtime to a very high number, but for technical reasons it's hard to reliably predict what that might be. The best initial value is simply the first value in the search and a convenient way to do that is to initialise to zero and handle that as a special case. This is a general programming technique, worth remembering.

char newest[PATH_MAX+1] = {0};
time_t mtime = 0;
int check_if_older(const char *path, const struct stat *sb, int typeflag) {
    if (typeflag == FTW_F && (mtime == 0 || sb->st_mtime < mtime)) {
        mtime = sb->st_mtime;
        strncpy(newest, path, PATH_MAX+1);
    }
    return 0;
}

I've made two other changes. See if you can work out why.

Upvotes: 3

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