V2671. MISRA. Pointers returned by the function 'localeconv' / 'getenv' / 'setlocale' / 'strerror' should be used as if they have pointer to const-qualified type.

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

This diagnostic rule is relevant only for C.

Pointers returned by localeconv, getenv, setlocale, and strerror functions should be used as pointers to the const-qualified type.

According to the C standard, behavior is undefined (C23, Annex J, J.2, Section 119, 121, 189) if a program modifies:

• an object of the lconv type via a pointer returned by localeconv;
• a string via a pointer returned by getenv, setlocale, or strerror.

The example:

char *GetPath(void)
{
  char *path = getenv("PATH"); // <=
  if (path == NULL)
  {
    return NULL;
  }

  for (size_t i = 0; i < strlen(path); ++i)
  {
    if (path[i] == '\\')
    {
      path[i] = '/';
    }
  }

  return path;
}

The value is obtained from the PATH environment variable using the getenv function. It returns a pointer to an internal buffer, and the code then replaces every \ character with / directly in that buffer. The modified buffer is returned from the function via a pointer. Since standard libraries use an internal buffer, other functions can use it. Its direct modification leads to undefined behavior.

A correct implementation involves copying the string into a separate buffer, which is then modified:

char *GetPath(void)
{
  const char * const path = getenv("PATH");
  if (path == NULL)
  {
    return NULL;
  }

  size_t len = strlen(path);
  char *buffer = malloc((len + 1) * sizeof(char));
  if (buffer == NULL)
  {
    return NULL;
  }

  buffer[len] = '\0';

  for (size_t i = 0; i < len; ++i)
  {
    if (path[i] == '\\')
    {
      buffer[i] = '/';
    }
    else
    {
      buffer[i] = path[i];
    }
  }

  return buffer;
}

This diagnostic is classified as:

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