Compilation error: “stddef.h: No such file or directory”

Question

Whenever I try to compile this code it always ends up with this error:

    In file included from /usr/include/wchar.h:6:0,
             from /usr/lib/gcc/i68         


        

Answer 1

When I was incorporating a software library written in C into an existing demo project(used a C++ mbed library) I encountered this problem. The demo project would compile just fine, but after I replaced the existing main file by my own, this error occurred.

At this point I hadn't yet thought about the fact that the mbed library that I needed was written in C++. My own main file was a .c file that #include the mbed header file. As a result I used my normal C source as if it was a C++ source. Therefore the compiler that was used to compile my main file was the C compiler. This C compiler then encountered a #include of a module that actually does not exist (within its scope), as it's not a C++ compiler.

Only after I inspected the output of the build log I realised the various source C and C++ files were compiled by more that 1 compiler(the c++ compiler). The project used used compilers arm-none-eabi-c++ and arm-none-eabi-gcc (for embedded systems) as seen below.

Compile log:

Building file: ../anyfile.cpp
Invoking: MCU C++ Compiler
arm-none-eabi-c++  "../anyfile.cpp"
Finished building: ../anyfile.cpp

Building file: ../main.c
Invoking: MCU C Compiler
arm-none-eabi-gcc  "../main.c"
In file included from \mbed/mbed.h:21:0,
                 from ../main.c:16:
\mbed/platform.h:25:19: fatal error: cstddef: No such file or directory
compilation terminated.

Of course in a C++ environment cstddef exists, but in a C environment cstddef doesn't exist, in stead it's just C's implementation of stddef.

In other words, cstddef does not exist in the C compiler. I resolved this problem by renaming my main.c file to main.cpp and the rest of the code compiled smoothly too.

TLDR/Conclusion: When building a C++ project, avoid mixing C files with C++ files(sources and headers). If possible rename .c files to .cpp files to use the C++ compiler in stead of the C compiler where required.