How to enable -fpermissive for a section of code - c++

Question

I have a C single-header library that I would like to use in my C++ project. Normally, I would just include the file and that would be fine because C++ is almost a superset of C. However, this library has a goto that jumps over an initialization, violating the C++ standard.
I can get around this be enabling the -fpermissive compiler flag on GCC, but I want the errors to trigger properly for the rest of my code.
Is there a way I can enable it just for this one header file (perhaps similar to #pragma GCC diagnostic XXX).

Answer 1

There's #pragma GCC optimize "blah" or the function attribute __attribute__((optimize("blah"))) that act like the argument -fblah was given for the rest of that file/that specific function, but it doesn't seem to work with -fpermissive:
$ cat foo.cpp
#pragma GCC optimize "permissive"
void foo(int x) {
}
$ g++-8 -c -Wall -Wextra foo.cpp
foo.cpp:1:22: warning: bad option ‘-fpermissive’ to pragma ‘optimize’ [-Wpragmas]
#pragma GCC optimize "permissive"
^~~~~~~~~~~~
foo.cpp:3:16: warning: bad option ‘-fpermissive’ to attribute ‘optimize’ [-Wattributes]
void foo(int x) {
One option would be to put the function that needs this in a file by itself, and configure your build system to compile just that file with -fpermissive, though that breaks the header-only model. Or fix the code so it doesn't need that option at all.

Answer 2

Per gcc man page:
-fpermissive
Downgrade some diagnostics about nonconformant code from errors to warnings. Thus, using -fpermissive allows some nonconforming code to compile.
So in theory, one can allow a section to compile as permissive using a sequence of gcc warning pragmas:
// Start permissive code
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-result"
#pragma GCC diagnostic ignored "-Wuninitialized"
// .. Other #pragmas
// Permissive Code here.
// Restore normal processing.
#pragma GCC diagnostic pop
One challenge is that there is no published list of errors that will be ignored with -fpermissive (At least I could not find it). One possible approach will be to compile the code, and enter the '#pragma's one at at a time, until the code compiles cleanly.
If one can identify all (or most) of the rules, possible to put them into #include file.
#pragma GCC diagostic push
#include "permissive.h"
// Permissive Code here
#pragma GCC diagostic pop