在串行通信的情况下，来自 tcgetattr 的错误 9 是什么

Question

I making ac program to read data from a serial device. I am getting 5 values from serial device and I have made a logic through which it is automatically updating values. It runs properly but after sometime it hangs and shows error error 9 from tcgetattr . I have used the code from one of the answers to this question http://tinyurl.com/keuxkgz Error is in the function void set_blocking (int fd, int should_block) and int set_interface_attribs (int fd, int speed, int parity) . I am not able to remove it. Please help. Thanks.!

Answer 1

I'm not going to look at external sources. However, errno == 9 == EBADF in Linux. It means your file descriptor ( fd ) is incorrect.

Instead of printing just errno , I recommend you use something like

if (...) {
    const int errnum = errno;
    fprintf(stderr, "%s: tcsetattr() failed: %s (%d)\n", devicepath, strerror(errnum), errnum);
    exit(EXIT_FAILURE);
}

where devicepath is the variable containing the path to the serial device you're using. (You need to #include <string.h> for strerror() , #include <errno.h> for errno , and #include <stdlib.h> for exit() and EXIT_FAILURE .)

Answer 2

This happened to me due to permission denial to open the serial port.