C: stdin and std * errs

Question

I want to manipulate Stdin, and then Std*. But I get the following errors:

$ gcc testFd.c                                                                 
testFd.c:9: error: initializer element is not constant
testFd.c:9: warning: data definition has no type or storage class
testFd.c:10: error: redefinition of `fd'
testFd.c:9: error: `fd' previously defined here
testFd.c:10: error: `mode' undeclared here (not in a function)
testFd.c:10: error: initializer element is not constant
testFd.c:10: warning: data definition has no type or storage class
testFd.c:12: error: syntax error before string constant

The program is shown below.

#include <stdio.h>
#include <sys/ioctl.h>

int STDIN_FILENO = 1;
// I want to access typed 
// Shell commands, dunno about the value:
unsigned long F_DUPFD;

fd = fcntl(STDIN_FILENO, F_DUPFD, 0);
fd = open("/dev/fd/0", mode);

printf("STDIN = %s", fd);

Updated errors: just trying to get a sample program on file descriptors for working in C, quite lost with an error report

#include <stdio.h>
#include <sys/ioctl.h>

int main (void) {
    int STDIN_FILENO;
    // I want to access typed 
    // Shell commands, dunno about the value:
    unsigned long F_DUPFD;
    int fd;
    const char mode = 'r';

    fd = fcntl(STDIN_FILENO, F_DUPFD, 0);
    /* also, did you mean `fopen'? */
    fd = fopen("/dev/fd/0", mode);

    printf("STDIN = %s", fd);

    return 0;
}

Program execution is shown below.

$ gcc testFd.c                                                                
testFd.c: In function `main':
testFd.c:14: warning: passing arg 2 of `fopen' makes pointer from integer without a cast
testFd.c:14: warning: assignment makes integer from pointer without a cast

Answer 1

Try using the method main:

#include <stdio.h>
#include <sys/ioctl.h>

int main (void) {
    int STDIN_FILENO = 1;
    // I want to access typed 
    // Shell commands, dunno about the value:
    unsigned long F_DUPFD;
    /* also, declare the type of your variable "fd" */
    int fd;

    fd = fcntl(STDIN_FILENO, F_DUPFD, 0);
    /* also, did you mean `fopen'? */
    fd = open("/dev/fd/0", mode);

    printf("STDIN = %s", fd);

    return 0;
}

Answer 2

You forgot your main function ()!

Answer 3

main()?

Answer 4

, main(), . STDIN_FILENO - ; .

Try to explain what you really want to do, with some details, and we can offer how to do it.