using dd command in c program

Question

I need to use the following code in my c code and compile.

dd if=/dev/urandom bs=1 count=400 of=/dev/udp/SrcAddress.ai_addr/8000

This is giving the error

‘dd’ was not declared in this scope

How can I use this command inside my c code?

Answer 1

You cannot use dd like that. Your C program is not a terminal and you cannot perform shell commands by just writing them in your code. One way to perform what you want is by using popen as following.

 #include <stdio.h>

 FILE *fd = popen("dd if=/dev/urandom bs=1 count=400 of=/dev/udp/SrcAddress.ai_addr/8000","w");
 pclose(fd);

Answer 2

It is possible that what you actually want to do is write the equivalent of this dd operation in C. That would look something like this.

int send_n_random_bytes_udp(unsigned int n, const struct sockaddr_in *dest)
{
    int rng = open("/dev/urandom", O_RDONLY);
    if (rng == -1) return -1;
    int sk  = socket(AF_INET, SOCK_DGRAM);
    if (sk  == -1) { close(rng); return -1; }

    int status = 0;
    for (unsigned int i = 0; i < n; i++) {
        char byte;
        if (read(rng, &byte, 1) != 1 ||
            sendto(sk, &byte, 1, 0,
                   (const struct sockaddr *)dest,
                   sizeof(struct sockaddr_in)) != 1) {
            status = -1;
            break;
        }
    }
    close(sk);
    close(rng);
    return status;
}