Compiling with g++

Last Updated : 08 Apr, 2024

g++ command is a GNU c++ compiler invocation command, which is used for preprocessing, compilation, assembly and linking of source code to generate an executable file. The different "options" of g++ command allow us to stop this process at the intermediate stage.

Check g++ compiler version information:

g++ --version

Compile a CPP file to generate executable target file: g++ file_name command is used to compile and create an executable file a.out (default target name).
Example: Given a simple program to print "Hello Geek" on standard output with file name hello.cpp

CPP

// hello.cpp file #include <iostream> int main() { std::cout << "Hello Geek\n"; return 0; }

g++ hello.cpp

This compiles and links hello.cpp to produce a default target executable file a.out in present working directory. To run this program, type ./a.out where ./ represents present working directory and a.out is the executable target file.

./a.out

g++ -S file_name is used to only compile the file_name and not assembling or linking. It will generate a file_name.s assembly source file.
Example:

g++ -S hello.cpp

g++ -c file_name is used to only compile and assemble the file_name and not link the object code to produce executable file. It will generate a file_name.o object code file in present working directory.
Example:

g++ -c hello.cpp

g++ -o target_name file_name: Compiles and links file_name and generates executable target file with target_name (or a.out by default).
Example:

g++ -o main.exe hello.cpp

Compile and link multiple files: When -c flag is used, it invokes the compiler stage which translates source code to object code.When -o flag is used it links object code to create the executable file from file_name.o to a.out(default), multiples files may be passed together as arguments.
Example:

CPP

// hello.cpp file #include "helloWorld.h" #include <iostream> int main() {     std::cout << "Hello Geek\n";     helloWorld();     return 0; }

CPP

// helloWorld.cpp file #include <iostream> void helloWorld() { std::cout << "Hello World\n"; }

CPP

// helloWorld.h file void helloWorld();

g++ -c helloWorld.cpp hello.cpp

It compiles and creates object code for the files helloWorld.cpp and hello.cpp to helloWorld.o and hello.o respectively.

g++ -o main.exe helloWorld.o hello.o

It links the object codes helloWorld.o and hello.o to create an executable file main.exe

./main.exe

It runs the executable file main.exe

g++ -Wall file_name: It prints all warning messages that are generated during compilation of file_name.
Example:

CPP

// hello.cpp file #include <iostream> int main() { int i; std::cout << "Hello Geek\n"; return 0; }

g++ -Wall hello.cpp

File extension for c++ files can be .cpp or .c++ , .cpp is widely used but .cpp and .c++ are exactly same and all above functionalities are same for .c++ too