Question

How to check in c , linux if a file has been updated/changed .

I want to check a file for update before opening the file and performing extraction/ i/o operations from it.

Answer 1

Look at the man page for stat(2). Get the st_mtime member of the struct stat structure, which will tell you the modification time of the file. If the current mtime is later than a prior mtime, the file has been modified.

An example:

int file_is_modified(const char *path, time_t oldMTime) {
    struct stat file_stat;
    int err = stat(path, &file_stat);
    if (err != 0) {
        perror(" [file_is_modified] stat");
        exit(errno);
    }
    return file_stat.st_mtime > oldMTime;
}

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Here’s an introduction to inotify, if that’s what you’re looking for.