# V2606. MISRA. There should be no attempt to write to a stream that has been opened for reading.

This diagnostic rule is based on the MISRA (Motor Industry Software Reliability Association) manual for software development.

This rule only applies to C. The C standard does not define the behavior when the 'fputs' function writes data into a read-only file. Therefore, this is an incorrect behavior.

Look at the example:

    void foo(void)
    {
      FILE *file = fopen("file.txt", "r");
      if (file != NULL)
      {
        fputs(file, "I am writing to the read-only file\n");
        fclose(file);
      }
    }

The file.txt file was opened in read-only mode, but at the same time the 'fputs' function writes data into it. The software may behave unpredictably in this situation.

Most likely it's a typo and you need to change the opening mode:

    void foo(void)
    {
      FILE *file = fopen("file.txt", "w");
      if (file != NULL)
      {
        fputs(file, "I am writing to the write-only file\n");
        fclose(file);
      }
    }

This diagnostic is classified as:

MISRA-C-2012-22.4 MISRA-C-2023-22.4