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C# vs. C++ Compile Time Benchmarks

Test Environment

  • 2.3 Ghz Intel Core i7-3615QM
  • Mac OS X 10.12.5
  • Unity 2017.2.0f3
  • Ninja 1.8.2
  • Apple LLVM version 8.1.0 (clang-802.0.42)
  • CMake 3.9.1

Compiled Sources

C++ sources consist of 1000 .cpp and .h files plus a Main.cpp consisting of a stub main function. Each .cpp file references its corresponding .h file with #include. Each .h file contains a struct definition with 100 int fields and 100 void Foo() methods. Each .cpp file contains the 100 method definitions for the corresponding .h file's struct.

C# sources consist of 1000 .cs files. Each contains a public class with 100 public int fields and 100 public void Foo() methods.

Each file starts with a one-line comment containing the timestamp. Each struct, class, field, and method is prefaced with a one-line comment. Indentation with tabs is present as with "normally"-formatted code.

Code Generator

A code generator written in C writes all of the source files to their appropriate directories. Running it updates all the files' timestamps so is a good way to force all source files to be recompiled.

To run the code generator, compile with clang -o Generator Generator.c then run it with ./Generator.

Compiling C#

C# code is placed in an otherwise empty Unity project's Assets directory by the code generator. Note that using the "Experimental (.NET 4.6 Equivalent)" option in "Project Settings > Player > Scripting Runtime Version" does not impact compile times. The project is then opened so all assets can be imported by Unity.

To do a full compile, run the code generator and switch to the Unity editor.

To compile just one file, add an "a" to the end of one .cs file's timestamp comment and switch to the Unity editor.

The Unity editor does not report compile times. To measure how long a compilation takes, start a stopwatch when either the "Importing Assets" dialog or the spinner in the bottm-right corner of the window appear. Stop the stopwatch when the spinner disappears.

Compiling C++

C++ code is placed in the CppSource directory by the code generator. A CMakeLists.txt file is already present in that directory. Run cmake -GNinja /path/to/CppSource to build the Ninja build configuration.

To do a full compile, run the code generator and then run time ninja to compile.

To compile just one file, add an "a" to the end of one .h file's timestamp comment then run time ninja to compile.

Results

Language Full Compile Compile One File
C# 7 seconds 3.5 seconds
C++ 5.360 seconds 0.223 seconds
C++ Speedup 1.31x 15.70x

Conclusion

A full compile of C++ is only marginally faster than C#, but incremental compiles are dramatically faster.