How do I compile with C++98 on MacOS?

Question

I need to use C++98 for university programs, however even when passing the -std=c++98 flag to clang++ or to g++ it still seems to compile with c++11 and does not give errors if I use c++11 features. Here is a simple example:

#include <string>
#include <sstream>
using namespace std;
int main()
{
    int i;
    string number = "12";
    i = stoi(number);
}

My makefile:

all:
    clang++ -std=c++98 -c *.cpp
    clang++ -o main *.o

clean:
    rm -f *.o main

run: clean all
    ./main

Then I run the command make from Terminal (I tried using clang++ instead of g++ but it yields the same result) and receive the following output:

➜  cppversion make
g++ -std=c++98 -c *.cpp
g++ -o main *.o
➜  cppversion make
clang++ -std=c++98 -c *.cpp
clang++ -o main *.o
➜  cppversion

I believe this code should not have compiled if the -std=c++98 flag was working. How do I force code to compile with c++98?

Here is the version of clang:

Apple clang version 12.0.5 (clang-1205.0.22.11)
Target: x86_64-apple-darwin20.2.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin\

Here is the version of g++:

Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/Library/Developer/CommandLineTools/SDKs/MacOSX11.1.sdk/usr/include/c++/4.2.1
Apple clang version 12.0.5 (clang-1205.0.22.11)
Target: x86_64-apple-darwin20.2.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

I have also tried adding the flag -pedantic but it does not fix the problem.

Using the flag -stdlib=libc++ yields the following:

➜  cppversion make
clang++ -stdlib=libstdc++ -std=c++98 -c *.cpp
clang: warning: include path for libstdc++ headers not found; pass '-stdlib=libc++' on the command line to use the libc++ standard library instead [-Wstdlibcxx-not-found]
main.cpp:1:10: fatal error: 'string' file not found
#include <string>
         ^~~~~~~~
1 error generated.
make: *** [all] Error 1

If I change it to just -stdlib=libc++ then it still compiles:

➜  cppversion make
clang++ -stdlib=libc++ -std=c++98 -c *.cpp
clang++ -o main *.o
➜  cppversion

I found an easy solution: Use homebrew to install gcc and use g++-11 to compile.

Answer 1

Try using -std=c++98 -pedantic.

This should strictly enforce the specific standard.