Challenge: What does this code do?

Here is a pretty simple C program, running on Linux. Can you tell me what you expect its output to be?#include #include #include #include #include #include #define BUFFER_SIZE (3ULL * 1024 * 1024 * 1024) // 3GB in bytes int main() { int fd; char buffer; struct stat st; buffer = (char )malloc(BUFFER_SIZE); if (buffer == NULL) { return 1; } fd = open("large_file.bin", O_WRONLY | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR); if (fd == -1) { return 2; } if (write(fd, buffer, BUFFER_SIZE) == -1) { return 3; } if (fsync(fd) == -1) { return 4; } if (close(fd) == -1) { return 5; } if (stat("large_file.bin", &st) == -1) { return 6; } printf("File size: %.2f GB\n", (double)st.st_size / (1024 * 1024 * 1024)); free(buffer); return 0; }And what happens when I run:head large_file.bin | hexdump -CThis shows both surprising behavior and serves as a good opening for discussion on a whole bunch of issues. In an interview setting, that can give us a lot of insight into the sort of knowledge a candidate has.

Jan 20, 2025 - 13:33

Here is a pretty simple C program, running on Linux. Can you tell me what you expect its output to be?

#include 
#include 
#include 
#include 
#include 
#include 


#define BUFFER_SIZE (3ULL * 1024 * 1024 * 1024) // 3GB in bytes


int main() {
    int fd;
    char *buffer;
    struct stat st;


    buffer = (char *)malloc(BUFFER_SIZE);
    if (buffer == NULL) {
        return 1;
    }


    fd = open("large_file.bin", O_WRONLY | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
    if (fd == -1) {
        return 2;
    }


    if (write(fd, buffer, BUFFER_SIZE) == -1) {
        return 3;
    }


    if (fsync(fd) == -1) {
        return 4;
    }


    if (close(fd) == -1) {
        return 5;
    }


    if (stat("large_file.bin", &st) == -1) {
        return 6;
    }


    printf("File size: %.2f GB\n", (double)st.st_size / (1024 * 1024 * 1024));


    free(buffer);
    return 0;
}

And what happens when I run:

head  large_file.bin  | hexdump -C

This shows both surprising behavior and serves as a good opening for discussion on a whole bunch of issues. In an interview setting, that can give us a lot of insight into the sort of knowledge a candidate has.

Challenge: What does this code do?

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