1. C Compiler Online Compiler
2. C Compiler For Windows
3. C Compiler Cannot Create Executables
4. C Compiler Download
5. C Compiler For Cygwin
6. Online C Compiler

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Table of Contents

• 1. Compiler flags and invocation
  • 1.1. GCC, GCC/Mingw and Clang++

C Compiler Online Compiler

1 Compiler flags and invocation

1.1 GCC, GCC/Mingw and Clang++

1.1.1 General Compiler and Linker Flags

Search Path and Library Linking Flags

• -l[linalg]
  • => Links to shared library or shared object - Specifically, itlinks to linalg.dll on Windows, liblinalg.so (on Unix-like oses likeLinux, BSD, AIX, …) or linalg.dylib on MacOSX.
• -L[/path/to/shared-libraries]
  • => Add search path to shared libraries, directory containing*.so, *.dll or *.dlyb files such as libLinearAlgebra.so dependingon the current operating system.
• -I[/path/to/header-files]
  • Add search path to header files (.h) or (.hpp).
• -D[FLAG] or -D[FLAG]=VALUE
  • Pass preprocessor flag #if FLAG …

GCC and Clang Most common compiler flags:

• std - Specify the C++ version or ISO standard version.
  • -std=c++11 (ISO C++11)
  • -std=c++14 (ISO C++14)
  • -std=c++1z (ISO C++17)
  • -std=c++20 (C++20 experimental)
  • -std=gnu++ (ISO C++ with GNU extensions)
• Verbosity - [W stands for warning]
  • -Wall
    • Turns on lots of compiler warning flags, specifically(-Waddress, -Wcomment, -Wformat, -Wbool-compare,-Wuninitialized, -Wunknown-pragmas, -Wunused-value,-Wunused-value …)
  • -Werror
    • Turn any warning into a compilation error.
  • -Wextra or just -W (see more)
    • Enables extra flags not enabled by -Wall, such as-Wsign-compare (C only), -Wtype-limits, -Wuninitialized …
  • -pendantic or -Wpendantic
    • Issue all warning required by ISO C and ISO C++ standard, itissues warning whenever there are compiler extensions noncompliant to ISO C or C++ standard.
  • -Wconversion
  • -Wcast-align
  • -Wunnused
  • -Wshadow
  • -Wold-style-cast
  • -Wpointer-arith -Wcast-qual -Wmissing-prototypes -Wno-missing-braces
• Output file: -o <outputfile>
  • g++ file.cpp -o file.bin
• Common library flags
  • -lm - Compiles against the shared library libm (basic mathlibrary, mostly C only)
  • -lpthread - Compile against Posix threads shared library
• Include Path - Directories containing headers files.
  • -I/path/to/include1 -I/path/to/include2 …
• Compilation flags -D<flag name>
  • -DCOMPILE_VAR -> Enable flag COMPILE_VAR - It is equivalent toadd to the code (#define COMPILE_VAR)
  • -DDO_SOMETHING=1 - Equivalent to add to the code #define DO_SOMETHING = 1
  • -DDISABLE_DEPRECATED_FUNCTIONS=0
• Optmization - docs
  • -O0
    • No optmization, faster compilation time, better for debugging builds.
  • -O2
  • -O3
    • Higher level of optmization. Slower compile-time, better forproduction builds.
  • -OFast
    • Enables higher level of optmization than (-O3). It enables lotsof flags as can be seen src (-ffloat-store, -ffsast-math,-ffinite-math-only, -O3 …)
  • -finline-functions
  • -m64
  • -funroll-loops
  • -fvectorize
  • -fprofile-generate
• Misc
  • -fexceptions -fstack-protector-strong –param=ssp-buffer-size=4
• Special Options
  • -g
    • => Builds executable with debugging symbols for GDB GNUDebugger or LLDB Clang/LLVM Debugger. It should only be usedduring development for debugging builds.
  • -c
    • => Compiler source(s) to object-code (input to linker). Thisoption is better for incremental compilation when usingmultiple files.
  • -pie
    • => Builds a dynamically linked position independent executable.
  • -static-pie
    • => Builds a staticlaly linked position independent executable.
  • -shared
    • => Build a shared library (.so or .dylib on U*nix-like Oses) or.dll on MS-Windows.
  • -fno-exceptions
    • => Disable C++ exceptions (it may be better for embedded systemsor anything where exceptiions may not be acceptable).
  • -fno-rtti
    • => Disable RTTI (Runtime Type Information) - There manytexts around where game and embedded systems developers reportthat they disable RTTI due to performance concerns.
  • -fvisibility=hidden
    • => Make library symbols hidden by default, in a similar way towhat happens in Windows DLLs where exported symbols must havethe prefix __declspec(dllexport) or __declspec(dllimport). Whenall symbols are exported by default, it may increase thelikelyhood of undefined behavior if there a multipledefinitions of same symbol during linking. See more at:
  • https://wiki.debian.org/Hardening
    • => Lots of compiler flags for hardening security.

Linker Flags

• Verbose
  • -Wl,–verbose
  • -Wl,–print-memory-usage
• Directory which linker will search for libraries (*.so files onUnix; *.dylib on MacOSX and *.dll on Windows)
  • -L/path/to-directory
• Strip Debug Information
  • -Wl,-s
• Build Shared Library
  • -shared
• Set Unix Shared Library SONAME (See)
  • –Wl,soname,<NAME>
  • –Wl,soname,libraryname.so.1
• General Format of Linker Options
  • -Wl,–<OPTION>=<VALUE>
• Windows-only (MINGW)
  • -Wl,–subsystem,console => Build for console subsystem.
  • -Wl,–subsystem,windows => Build for winodw subsystem.
  • -ld3d9 => Link against DirectX (d3d9.dll)
• Windows-only DLL (Dynamic Linked Libraries)
  • -shared
  • -Wl,–export-all-symbols
  • -Wl,–enable-auto-import

• Static link against LibGCC runtime library:
  • -static-libgcc
• Static link against libstdC++ runtime library:
  • -static-libstdc++
• Static link against Gfortran (GNU fortran) runtime library.
  • -static-libgfortran
• Set Unix RPATH (Note Windows does not have rpath)
  • –Wl,rpath=/path/to/directory1;/path/to/directory2
• Set Unix RPATH to executable current directory.
  • –Wl,rpath=$ORIGIN
• Change the default dynamic linker (UNIX and Linux)
  • -Wl,-dynamic-linker,/path/to/linker/ld-linux.so.2.1
• Common Unix Dependencies:
  • -lpthread => Link against POSIX threads library.
  • -ldl => Link against libdl library for dlopen(), dlclose(), APIs.
• Exclude Runtime Libraries (gcc docs)
  • -nostartfiles => 'Do not use the standard system startup files when linking. The standard system libraries are used normally, unless -nostdlib, -nolibc, or -nodefaultlibs is used.'
  • -nodefaultlibs => Do not use the standard system libraries when linking.
  • -nolibc => Do not use the C library or system libraries tightly coupled with it when linking.
  • -nostdlib => Do not use the standard system startup files or libraries when linking.
• Set heap size
  • -Wl,–heap,201561
• Stack reserve size
  • -Wl,–stack,419525
• Generate Linker Map (mostly used for embedded systems)
  • -Wl,-Map=linker-map.map
• Use a custom linker script (embedded systems)
  • -Wl,T/path/to/linker-script.ld
• Linker version script
  • -Wl,–version-script,criptfile
• Eliminate dead-code or unused code for decreasing the program orfirmware size (embedded systesm) - (Elinux)
  • -ffunction-sections -fdata-sections -Wl,–gc-sections
• Miscellaneous
  • -Wl,–allow-multiple-definition
  • -fno-keep-inline-dllexport
  • -Wl,–lager-address-aware
  • -Wl,–image-base,358612

Files Generated by the Compiler

• Object Files
  • *.o -> Generated on *NIX - Linux, MacOSX … by GCC or Clang
  • *.obj -> Windows
• Binary Native Executable - Object Code
  • *NIX: Linux, MacOSX, FreeBSD -> Without extension.
  • Windows: *.exe
  • *.hex -> Extension of many compiled firmwares generated byembedded systems compilers such as proprietary compilers forMicrocontrollers.
• Shared Objects - Shared Libraries
  • *.dll -> Called dynamic linked libraries on Windows -> libplot.dll
  • *.so -> Called shared Object on Linux -> libplot.so
  • *.dylib -> Extension used on MacOSX.
• Static Library
  • *.a - extension

Review See:

• GNU Linker Command Language => GNU Linker Script Command Language,widely used for embedded systems.
• Removing Unused Functions and Dead Code (Washigton University)
• The why and how of RPATHs - Flameeyes
• Building and Using DLLs Prev Chapter 4. Programming with Cygwin (MINGW - Windows)

1.1.2 Peformance Optimization Flags

Levels of Optimization

• (-O0) - Optimization Level 0 (No optimization, default)
  • Better for debugging builds during development, since itprovides faster compile-time.
• (-O1) - Optimization Level 1
• (-O2) - Optimization Level 2
  • Enables (-O1); inline small functions;
• (-O3) - Optimization Level 3 (Most aggressive optimization,Highest level of optmization and speed)
  • Problem: Slower compile-time and large binary size.
  • More function inlining; loop vectorization and SIMD instructions.
• (-OS) - Code Size Optimization
  • Enable (-O2), but disable some optimizations flags in order toreduce object-code size.
• (-Oz) [CLANG-ONLY] - Optimizes for size even further than (-OS)
• (-Ofast) - Activate (-O3) optimization disregarding strictstandard compliance.
• (-Og) - Optmizing for debugging.
  • Enables all optimization that does not conflicts withdebugging. It can be used with the (-g) flag for enablingdebugging symbols.

Other Optimization Flags

Linking:

• Link Time Optimization
  • (-flto)

Loops and Vectorization:

• Unroll loops
  • -funroll-loop
• Auto Vectorization
  • (-O3) or (-ftree-vectorize)
• Verbose Auto Vectorization
  • (-ftree-vectorizer-verbose)

Misc:

• Profiling Information for further processing and measuringperformance with gprof program:
  • (-pg)
• Tune to Pentium 4 everything about the produced code.
  • -mcpu=pentium4
• Generate instructions for Pentium 4
  • -march=pentium4
• Attempt to Inline All Functions, even if they are not annotatedwith inlining. Note: inlining trades speed for increasing of code size.
  • -finline-functions
• Devirtualize - attempt to convert vritual function calls to directcalls. Enabled by: (-O2), (-O3) and (-Os).
  • -fdevirtualize
• Hide Global Sysmbols by default in shared libraries
  • Note: it equires the exposed symbols to be annotated with GGCextension __attribute__(...). Benefits: decreases startup time;quickier function calls; smaller memory footprints.
  • (-fvisibility=hidden)
  • -Bsymbolic

Further Reading

• Optimizing Floating Point Calculations II - Michael A. Saum.
• Faster C++ - Cambridge University
• Using the GNU Compiler Collection (GCC): Optimize Options
  • Shows many GCC optimization options.
• A story about –fast-math -fbroken-math
  • Reports bugs that the optimization –fast-math may cause.
• Redis Benchmarks with Optimizations
  • Explains the optimization flag (-flto)
• Cache-Friendly Profile Guided Optimization - Baptiste Wicht
• Performance Optimization Getting your programs to run faster CS 691.
• Pragmatic Optimization in Modern Programming - Mastering Compiler Optimizations - Marina Kolpakova

1.1.3 Useful compiler switches for reducing binary size

Note: Those switches/flags are also useful for embedded systems.

1.1.6 Example - Build executable with unified compilation

Compile file1.cpp, file.cpp, file2.cpp into the executable app.bin

• Option 1: Compile and link once in a single command. Thedisadvantage of this way is the slower compile time rather thanseparate compilation and linking.

Explanation:

• -std=c++14 -> Set the C++ version. This flag can be C++11, C++14,C++17, C++20 …
• -o app.bin -> Set the output native executable file ot app.bin
• -I./include/path1/with/headers
  • Directory with header files
• -g Produce executable with debug symbols
• -Wall -Wextra -Wshadow
  • Warning flags - enable more verbosity which helps to catch bugsearlier.
• -O3 - Use optmization of level 3 - the disadvantage of usingoptmization is the slower compile time. So this flag should only beenabled on production builds.
• -lpthread -lblas -lboost_system-lboost_filesystem
  • Link against shared libraries (extensions: *.so - Unix, *.dylibor *.dll on Windows) pthread, blas, boost_system …

1.1.8 Release / Debug building

Compiler:

• GCC and CLANG
  • Debug: No optmized, but faster building time.
    • -OO -g
  • Release:
    • -O3 -s -DNDEBUG [-march=native] [-mtune=native]
    • -O2 -s -DNDEBGU
• MSVC:
  • Debug:
    • /MDd /Zi /Ob0 /Od /RTC1
  • Release:
    • /MD /O1 /Ob1 /DNDEBUG

Note:

• For GCC and Clang
  • -OO means no optmization
  • -g - adds debugging symbols to executable.
  • -DNDEBUG - disable assertions

References:

1.2 MSVC (VC++ or Visual C++) Compiler Options

C Compiler For Windows

MSVC Native tools:

C Compiler Cannot Create Executables

• CC = cl.exe
  • C and C++ Compiler - Can compile both C and C++ code depending onthe flag. By default it compiles C++ code.
• rc.exe => Resource Compiler.
• LD = link.exe
  • C++ Linker.
• AS = ml
  • Assembler
• AR = lib
  • Archiver

Compiler: cl.exe

C Compiler Download

• /nologo - Suppress microsoft's logo
• /out:<file.exe> - Set output file name.
• /EHsc
• /Zi - Add debugging symbols to the executable
• /c - Doesn't link generating *.exe or *.dll, it creates onlyintermedidate object code for further separate linking. It isuseful for compiling large code bases where each compilation unitcan be compiled separately.
• /W4 - Set the level of warning to the highest.
• /entry:<entrypoint> - Set the C/C++ runtime, it can be:
  • mainCRTStartup => calls main(), the entrypoint for console mode apps
  • wmainCRTStartup => calls wmain(), as above but the Unicode version
  • WinMainCRTStartup => calls WinMain(), the entrypoint for native Windows apps
  • wWinMainCRTStartup => calls wWinMain(), as above but the Unicode version
  • _DllMainCRTStartup => Calls DLLMain()
• /subsystem:<type> - Set the subsystem - default Console, it can be:
  • /subsystem:console - For applications that necessarly runs in theconsole (aka terminal emulator)
  • /subsystem:windows - Doesn't display the cmd.exe terminal whenones click at the application executable.
• /TC -> Specify that file name is C source code
• /TP -> Specify that file name is a C++ source code (default)
• /MD, /MT, /LD => Run-time library - Indcates that object-code(compiled program) is a DLL.
• /GF -> (Eliminate Duplicate Strings) - Enables the compiler tocreate a single copy of identical strings in the program image andin memory during execution. This is an optimization called stringpooling that can create smaller programs.

CRT C Runtime Options

• Static Linking: The library is appended to the executable, only asingle file, the executable needs to be deployed.
• Dynamic Linking: The library is DLL shared library and not appendedto the executable. The executable needs to be deployed with thelibrary.

C Compiler For Cygwin

See:

Useful preprocessor:

• Set subsystem

• Set linker library to be linked. This pragma is particularly usefulin graphical applications.

Examples:

Online C Compiler

• Compile multiple files generating an executable named out.exe. Notethe default subsystems is the console (/subsystem:console) and thedefault entry point is (mainCRTStartup).
  • /Isrc/includes => Directories containing header files
  • /ld or /linker => Linker flags
  • && out.exe => If the compilation is successful runs thegenerated executable out.exe

• Compile multiple files for windows subsystem (GUI app) and withwmainCRtstartup.

References:

See also: