When to Use gcc vs g++: Key Differences and Compilation Tips

Source: C Language Chinese Network; Edited by strongerHuang

As of September 2020, the GCC compiler has reached version 10.2 and can compile many languages, including C, C++, Go, Objective‑C, Fortran, Ada, D, and more. This tutorial focuses on compiling C and C++ programs.

To compile a C program, use the gcc command; for C++ programs, use g++. Although gcc can also compile C++ code, and g++ can compile C code, they differ in default behavior based on file extensions.

Files ending with .c are compiled as C by default.

Files ending with .cpp are compiled as C++ by default.

Files ending with .m are compiled as Objective‑C.

Files ending with .go are compiled as Go.

You can manually specify the language with the -x option, e.g., gcc -xc demo.c for C or gcc -xc++ demo.cpp for C++.

When using g++, the compiler always treats the source as C++ regardless of the file extension. This leads to stricter syntax checking compared to gcc. For example, the following C code compiles with gcc but produces errors with g++:

// demo.c
#include <stdio.h>
int main() {
    const char *a = "abc";
    printStr(a);
    return;
}
int printStr(const char* str) {
    printf(str);
}

Compiling with gcc -xc demo.c succeeds, while g++ demo.c reports three errors because C++ enforces stricter standards.

Conversely, compiling a simple C++ program that uses the standard library with gcc fails to link the required libraries:

// demo.cpp
#include <iostream>
#include <string>
using namespace std;
int main(){
    string str = "C语言中文网";
    cout << str << endl;
    return 0;
}

Running g++ demo.cpp succeeds, but gcc demo.cpp yields undefined reference errors. To compile C++ code with gcc, add the standard C++ library explicitly: gcc -xc++ -lstdc++ -shared-libgcc demo.cpp.

Thus, g++ is effectively equivalent to gcc -xc++ -lstdc++ -shared-libgcc, offering a convenient shortcut.

In summary, use gcc for C programs and g++ for C++ programs to avoid language‑specific issues and linking problems.