strerror_r

Header file:

    stdio.h

Synopsis:

    char * strerror_r (int errnum, char *buf, size t n)

Description:

    It is similar to strerror and it returns a string describing the error number.

    It is thread safe and mostly used in multi-threaded programs.

Sample Program for strerror_r in C:

---

  #include<stdio.h>

  #include<string.h>

  #include<errno.h>

  int main(int argc, char **argv) {

        FILE *fp;

        char buffer[50];

        int err;

        fp = fopen(argv[1], "r");

        if (fp == NULL) {

                /* errno - available in errno.h */

                err = strerror_r(errno, buffer, 50);

                printf("Error message=> %s\n", buffer);

                printf("Return value: %d\n", err);

                return;

        }

        fclose(fp);

        return 0;

  }

  Output:

  jp@jp-VirtualBox:~/cpgms/chap2$ ls

  a.out  strerror.c  strerror_r.c  strerror_r_ts.c

  jp@jp-VirtualBox:~/cpgms/chap2$ ./a.out jp.txt

  Error message=> No such file or directory

  Return value: 0

  jp@jp-VirtualBox:~/cpgms/chap2$

Sample program for strerror_r in threads:

---

  #include<stdio.h>
  #include<string.h>
  #include<errno.h>
  #include<pthread.h>

  pthread_t thread_id;

  void *
  thr_fn(void *errnum)
  {
        char buffer[256];
        int err;
        err = strerror_r(*((int *)errnum), buffer, 256);
        printf("Error: %s\n", buffer);
        printf("Return value:%d\n", err);
        return ((void *)0);
  }

  int
  main(int argc, char **argv)
  {
        FILE *fp;
        int err;
        fp = fopen(argv[1], "r");
        if (fp == NULL) {
                err = pthread_create(&thread_id, NULL, thr_fn, &errno);

                if (err != 0)
                        printf("can't create thread: %s\n", strerror(err));
        }
        sleep(1);
        return 0;

  }

  Output:

  jp@jp-VirtualBox:~/cpgms/chap2$ gcc strerror_r_ts.c -lpthread
  jp@jp-VirtualBox:~/cpgms/chap2$ ls
  a.out  strerror.c  strerror_r.c  strerror_r_ts.c
  jp@jp-VirtualBox:~/cpgms/chap2$ ./a.out jp.txt
  Error: No such file or directory
  Return value:0
  jp@jp-VirtualBox:~/cpgms/chap2$