Compiling C++-code without a file

Question

I'm trying to compile some C++ code using your standard g++ compiler. However, rather than compiling from a file:

main.cpp:

#include <iostream>

int main(){
    std::cout << "Hello World!\n";
    return 0;
}

I would prefer to do something like

g++ ... "#include <iostream>\n int main(){ std::cout << \"Hello World!\n\"; return 0;}"

A previous post from stackoverflow showed that

echo "int main(){}" | gcc -Wall -o testbinary -xc++ -

works but I would like to know how it works and better yet, if there is a way to do this without the need to pipe the contents.

EDIT:

I'm doing run-time code generation where I need to generate a shared library and load the functions created.

I thought there would be a flag to tell the compiler "hey, I'm giving you the source code and not the file".

Thanks again for the help!

Answer 1

echo "int main(){}" | gcc -Wall -o testbinary -xc++ -

works but I would like to know how it works and better yet, if there is a way to do this without the need to pipe the contents.

Alternatively you can say (e.g. in a shell-script):

gcc -Wall -o testbinary -xc++ - << EOF
int main(){}
EOF

Answer 2

The compiler reads from an input source - either the stdin or a file supplied. You need a pipe to supply something from elsewhere to the compiler. There is no other choice (and of course, some compilers may not have an option to read from stdin either)