What is the difference between g++ and gcc?

Question

gcc and g++ are compiler-drivers of the GNU Compiler Collection (which was once upon a time just the GNU C Compiler).

Even though they automatically determine which backends (cc1 cc1plus ...) to call depending on the file-type, unless overridden with -x language, they have some differences.

The probably most important difference in their defaults is which libraries they link against automatically.

According to GCC's online documentation link options and how g++ is invoked, g++ is equivalent to gcc -xc++ -lstdc++ -shared-libgcc (the 1st is a compiler option, the 2nd two are linker options). This can be checked by running both with the -v option (it displays the backend toolchain commands being run).

GCC: GNU Compiler Collection

• Referrers to all the different languages that are supported by the GNU compiler.

gcc: GNU C      Compiler
g++: GNU C++ Compiler

The main differences:

1. gcc will compile: *.c\*.cpp files as C and C++ respectively.
2. g++ will compile: *.c\*.cpp files but they will all be treated as C++ files.
3. Also if you use g++ to link the object files it automatically links in the std C++ libraries (gcc does not do this).
4. gcc compiling C files has fewer predefined macros.
5. gcc compiling *.cpp and g++ compiling *.c\*.cpp files has a few extra macros.

Extra Macros when compiling *.cpp files:

#define __GXX_WEAK__ 1
#define __cplusplus 1
#define __DEPRECATED 1
#define __GNUG__ 4
#define __EXCEPTIONS 1
#define __private_extern__ extern

For c++ you should use g++.

It's the same compiler (e.g. the GNU compiler collection). GCC or G++ just choose a different front-end with different default options.

In a nutshell: if you use g++ the frontend will tell the linker that you may want to link with the C++ standard libraries. The gcc frontend won't do that (also it could link with them if you pass the right command line options).

What is the difference between g++ and gcc?

gcc has evolved from a single language "GNU C Compiler" to be a multi-language "GNU Compiler Collection". The term gcc may still sometimes refer to the "GNU C Compiler" in the context of C programming.

man gcc

# GCC(1)                     GNU
# 
# NAME
#        gcc - GNU project C and C++ compiler

However, g++ is the C++ compiler for the GNU Compiler Collection. Like gnat is the Ada compiler for gcc. see Using the GNU Compiler Collection (GCC)

For example, the Ubuntu 16.04 and 18.04 man g++ command returns the GCC(1) manual page.

The Ubuntu 16.04 and 18.04 man gcc states that ...

g++ accepts mostly the same options as gcc

and that the default ...

... use of gcc does not add the C++ library. g++ is a program that calls GCC and automatically specifies linking against the C++ library. It treats .c, .h and .i files as C++ source files instead of C source files unless -x is used. This program is also useful when precompiling a C header file with a .h extension for use in C++ compilations.

Search the gcc man pages for more details on the option variances between gcc and g++.

Which one should be used for general c++ development?

Technically, either gcc or g++ can be used for general C++ development with applicable option settings. However, the g++ default behavior is naturally aligned to a C++ development.

The Ubuntu 18.04 'gcc' man page added, and Ubuntu 20.04 continues to have, the following paragraph:

The usual way to run GCC is to run the executable called gcc, or machine-gcc when cross-compiling, or machine-gcc-version to run a specific version of GCC. When you compile C++ programs, you should invoke GCC as g++ instead.

One notable difference is that if you pass a .c file to gcc it will compile as C.

The default behavior of g++ is to treat .c files as C++ (unless -x c is specified).

Although the gcc and g++ commands do very similar things, g++ is designed to be the command you'd invoke to compile a C++ program; it's intended to automatically do the right thing.

Behind the scenes, they're really the same program. As I understand, both decide whether to compile a program as C or as C++ based on the filename extension. Both are capable of linking against the C++ standard library, but only g++ does this by default. So if you have a program written in C++ that doesn't happen to need to link against the standard library, gcc will happen to do the right thing; but then, so would g++. So there's really no reason not to use g++ for general C++ development.