glibc shadows gcc's C++ headers

When compiling C++ programs, glibc's include directory takes precedence

over gcc's for standard C headers like math.h, but glibc's headers

aren't completely compatible with C++. For example, isnan from math.h is

supposed to be a function, but glibc defines it as a macro.

This program demonstrates the problem:

#include <math.h>

int main(void) { int isnan(0); return isnan; }

It works as expected when gcc's built-in C++ headers are used, but not

if glibc is installed:

% guix environment --pure --ad-hoc gcc -- g++ -E isnan.cpp | tail -n1

int main (void) { int isnan (0); return isnan; }

% guix environment --pure --ad-hoc gcc glibc -- g++ -E isnan.cpp | tail -n1

int main (void) { int __builtin_isnan (0); return isnan; }

As a temporary workaround, I'm using the following package as a

replacement for glibc, to keep the glibc headers out of $CPATH. If it's

installed along with gcc, ld-wrapper and binutils, the test program

compiles without errors.

(use-modules (guix) (gnu))

(use-package-modules base)

(package

(inherit glibc)

(name "my-glibc")

(arguments

(substitute-keyword-arguments (package-arguments glibc)

((#:phases phases)

`(modify-phases ,phases

(add-after 'install 'move-include

(lambda _

(rename-file (string-append %output "/include")

(string-append %output "/include-glibc"))

#t)))))))

Hello,

Robin Templeton <robin@igalia.com> writes:

Thanks for the report. Nowadays the recommended way to install the

GCC-based toolchain is to use the 'gcc-toolchain' package. The 'gcc'

package is now even made hidden in Guix, which doesn't seem to have this

particular issue:

$ guix environment --pure --ad-hoc gcc-toolchain -- g++ -E /tmp/isnan.cpp | tail -n1

int main(void) { int isnan(0); return isnan; }

$ guix environment --pure --ad-hoc gcc-toolchain glibc -- g++ -E /tmp/isnan.cpp | tail -n1

int main(void) { int isnan(0); return isnan; }

I'm closing this issue, but feel free to open a fresh one if you still

encounter problems.

Thank you,

Maxim