C- Need to simulate stdin within the code when calling a function

while( (reader=fread(array, sizeof(char), size, stdin))>0 )

I have this kind of guard what I need is within this cycle when 开发者_JAVA百科I call a function I want to simulate that I'm giving my fread something.

Sorry about the scary English.

---

@Fritschy's answer with @Ben Voigt's comment constitute the portable solution.

If you're on Unix/Linux/similar, you can actually write things into stdin by

int p[2];

// error return checks omitted
pipe(p);
dup2(p[0], STDIN_FILENO);

FILE *stdin_writer = fdopen(p[1], "w");

Now write into stdin_writer.

See pipe, dup2, fdopen in the POSIX standard.

---

You can replace stdin with a FILE* of your choice for testing:

FILE *test = fopen("mytestFile.txt", "r");
/* your code here... */

Or when need of stdin:

FILE *test = stdin;
/* your code here... */

---

This answer is constructed on @Ben Voigt's comment. Create input.txt with some text and main.c with this code. The code will inject input.txt text into stdin and then send it into stdout.

#include <stdlib.h>
#include <stdio.h>

int main() {
    freopen("input.txt", "r", stdin);

    unsigned int BLOCK_SIZE = 3;
    char buffer[BLOCK_SIZE];

    for (;;) {
        size_t bytes = fread(buffer, sizeof(char), BLOCK_SIZE, stdin);
        fwrite(buffer, sizeof(char), bytes, stdout);
        fflush(stdout);
        if (bytes < BLOCK_SIZE)
            if (feof(stdin))
                break;
    }

    return 0;
}