Compiling with GCC
suggest changeAssuming a single source file named main.cpp
, the command to compile and link an non-optimized executable is as follows (Compiling without optimization is useful for initial development and debugging, although -Og
is officially recommended for newer GCC versions).
g++ -o app -Wall main.cpp -O0
To produce an optimized executable for use in production, use one of the -O
options (see: -O1
, -O2
, -O3
, -Os
, -Ofast
):
g++ -o app -Wall -O2 main.cpp
If the -O option is omitted, -O0, which means no optimizations, is used as default (specifying -O without a number resolves to -O1).
Alternatively, use optimization flags from the O
groups (or more experimental optimizations) directly. The following example builds with -O2
optimization, plus one flag from the -O3
optimization level:
g++ -o app -Wall -O2 -ftree-partial-pre main.cpp
To produce a platform-specific optimized executable (for use in production on the machine with the same architecture), use:
g++ -o app -Wall -O2 -march=native main.cpp
Either of the above will produce a binary file that can be run with .\app.exe
on Windows and ./app
on Linux, Mac OS, etc.
The -o
flag can also be skipped. In this case, GCC will create default output executable a.exe
on Windows and a.out
on Unix-like systems. To compile a file without linking it, use the -c
option:
g++ -o file.o -Wall -c file.cpp
This produces an object file named file.o
which can later be linked with other files to produce a binary:
g++ -o app file.o otherfile.o
More about optimization options can be found at gcc.gnu.org. Of particular note are -Og
(optimization with an emphasis on debugging experience – recommended for the standard edit-compile-debug cycle) and -Ofast
(all optimizations, including ones disregarding strict standards compliance).
The -Wall
flag enables warnings for many common errors and should always be used. To improve code quality it is often encouraged also to use -Wextra
and other warning flags which are not automatically enabled by -Wall
and -Wextra
.
If the code expects a specific C++ standard, specify which standard to use by including the -std=
flag. Supported values correspond to the year of finalization for each version of the ISO C++ standard. As of GCC 6.1.0, valid values for the std=
flag are c++98
/c++03
, c++11
, c++14
, and c++17
/c++1z
. Values separated by a forward slash are equivalent.
g++ -std=c++11 <file>
GCC includes some compiler-specific extensions that are disabled when they conflict with a standard specified by the -std=
flag. To compile with all extensions enabled, the value gnu++XX
may be used, where XX
is any of the years used by the c++
values listed above.
The default standard will be used if none is specified. For versions of GCC prior to 6.1.0, the default is -std=gnu++03
; in GCC 6.1.0 and greater, the default is -std=gnu++14
.
Note that due to bugs in GCC, the -pthread
flag must be present at compilation and linking for GCC to support the C++ standard threading functionality introduced with C++11, such as std::thread
and std::wait_for
. Omitting it when using threading functions may result in no warnings but invalid results on some platforms.
Linking with libraries:
Use the -l
option to pass the library name:
g++ main.cpp -lpcre2-8
#pcre2-8 is the PCRE2 library for 8bit code units (UTF-8)
If the library is not in the standard library path, add the path with -L
option:
g++ main.cpp -L/my/custom/path/ -lmylib
Multiple libraries can be linked together:
g++ main.cpp -lmylib1 -lmylib2 -lmylib3
If one library depends on another, put the dependent library before the independent library:
g++ main.cpp -lchild-lib -lbase-lib
Or let the linker determine the ordering itself via --start-group
and --end-group
(note: this has significant performance cost):
g++ main.cpp -Wl,--start-group -lbase-lib -lchild-lib -Wl,--end-group