Feeding data from C to Python in Ubuntu-CodePudding

I'm trying to generate numbers in C, then pass them onto python, and print the data using sys.stdin. The code for generating numbers in C is this,

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <time.h>
#include <Windows.h>

int main() {
        unsigned int i;

        srand(time(NULL));

        while (1) {
                i = random() % 15000;
                printf("%u.u", i / 1000, i % 1000);
                printf("\n");
                usleep(100 * 1000);
        }
}

and the program for reading and printing this in python is this:

import sys

while(1):
    for line in sys.stdin:
        print(line[:-1])

Then, after I compile the c file gcc gen.c, I pipe it into python ~/a.out | python3 new.py. However, this only works when I delete the usleep part in the C code. When I delete the usleep bit, it works fine, but with the usleep part, it does not print anything and it seems that it gets stuck in line 4 in new.py.

CodePudding user response：

You just need to flush the output. The reason is explained in Why does stdout need explicit flushing when redirected to file?, i.e. the piping changes the buffering behavior.

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <time.h>
//#include <Windows.h>

int main() {
        unsigned int i;

        srand(time(NULL));

        while (1) {
                i = random() % 15000;
                printf("%u.u", i / 1000, i % 1000);
                printf("\n");
                fflush(stdout);
                usleep(1000 * 1000);

        }
}

$ gcc gen.c -o gen       
$ ./gen  | python3 new.py
14.383
0.886