format not a string literal and no format arguments

Taken from: http://bobthegnome.blogspot.com/2009/07/format-not-string-literal-and-no-format.html

Some time ago GCC started producing warnings like this:

warning: format not a string literal and no format arguments

What does this mean? GCC is saying that a function in printf style has a format string that it cannot check matches the format arguments. Here is some common code GLib code that causes this error:

GError *error = ...;
g_error(error->message);

Why is this a problem? As error->message cannot be checked it may contain a printf flag sequence, e.g. "Invalid data: 'g^y#%s'" (i.e. %s) that would cause run-time to try and access a non-existent argument. It could be worse and the format string could be user-input that is attempting to exploit your program.

So the solution is to always use a string literal for formatting like this:

g_error("%s", error->message);