Programming

$ cat > file_nums.c <<EOF
#include <stdio.h>
#include <unistd.h>

int main(void)
{
        printf("STDIN_FILENO=%d\n", STDIN_FILENO);
        printf("STDOUT_FILENO=%d\n", STDOUT_FILENO);
        printf("STDERR_FILENO=%d\n", STDERR_FILENO);
}

EOF

$ gcc file_nums.c -o file_nums

$ ./file_nums

STDIN_FILENO=0
STDOUT_FILENO=1
STDERR_FILENO=2

$

int fd=open("filename", O_RDWR|O_CREAT|O_TRUNC, 0660);
write(fd, ...);

#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>


int main(void)
{
    //FILE*out;        
    ssize_t ret;
        char buf[512];
        int fd=open("/dev/ttyUSB1", O_RDWR);
    int out = open("/home/hectromasencio/Desktop/prueba.txt", O_RDWR|O_CREAT|O_TRUNC);
        if(fd < 0) return(1);
//commands to start streaming data
        write(fd, "#o1\n", 4);
    sleep(3);
//command to stop streaming data
    write(fd, "#o0\n",4);

        while( (ret=read(fd, buf, 512)) > 0)
                write(out, buf, ret);
        //fwrite(buf,4,sizeof(buf),out);
//STDOUT_FILENO "/home/hectormasencio/Desktop/prueba.txt"
        close(fd);
        return(0);
}