Compiler ignoring std option for C files (only works on c++ files)

ocgltd

I have a project which mixes some older C and newer C++ files. I have set CONFIG=c++14 in my pro file. And interestingly the whole project compiles fine under Fedora 34.

However, on CentOS 7 the C files fail to compile (cause is variables declared in for loop). I confirmed that on CentOS 7 the compiler g++ has -std=gnu++1y option for my C++ files, and gcc (with no std option) for C files. So I assume it's using the oldest C standard by default.

How can I tell my qmake file to to use a later std option for my C files? (like std c99 or gnu99 or whatever is most recent)

ChrisW67

The default CentOS 7 GCC versions is 4.8.5 IIRC. C language support is c90 and c95 (complete), and incomplete c99 and c11 support. You might have something more recent.

If the CONFIG option above does not work then you could manually add the flag to QMAKE_CFLAGS (but not QMAKE_CXXFLAGS). You can find the necessary switch details https://gcc.gnu.org/onlinedocs/gcc-4.8.5/gcc/Standards.html#Standards

jeremy_k

The qmake variable reference lists c99 and c11 values for CONFIG.

ocgltd

@jeremy_k I googled for an example but couldn't find one, but are you saying

CONFIG += c++14 c11

is the solution ? I have been chasing QMAKE_CFLAG or similar

jeremy_k

Try it and come back with the result. The build will give you an answer in less time than any message board.

ChrisW67

The default CentOS 7 GCC versions is 4.8.5 IIRC. C language support is c90 and c95 (complete), and incomplete c99 and c11 support. You might have something more recent.

If the CONFIG option above does not work then you could manually add the flag to QMAKE_CFLAGS (but not QMAKE_CXXFLAGS). You can find the necessary switch details https://gcc.gnu.org/onlinedocs/gcc-4.8.5/gcc/Standards.html#Standards

ocgltd

@ChrisW67 I got it working with QMAKE_CFLAG setting to c11

Not sure what I compiles fine in some distro without this, but at least this is the solution for others