std::string to int benchmark

we compare different technics to convert std::string to int :

• naive atoi
• atoi
• std::stoi
• std::stringstream
• boost::lexical_cast
• boost::spirit::qi::parse

For measuring speed, google benchmark is used (https://github.com/google/benchmark) Only the difference between functions are significant

Environment

Required tools and libraries

• cmake >= 3.5.1
• gcc >= 5.4.0
• clang >= 3.8.0
• libboost-all-dev >= 1.58.0

debian installation

apt-get install cmake g++ clang libboost-all-dev

Source recovery

git clone https://github.com/benoit-bst/stringToIntBenchmark
cd StringtoIntBenchmark 
git submodule update --init

Compilation

mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=RELEASE ..
make

if you want to compile with clang, add -DCMAKE_CXX_COMPILER="/usr/bin/clang++" option

Run benchmark

for each function, we test 7 sizes of string (1->7)

./StringToIntBenchmark --benchmark_out=results --benchmark_out_format=csv

./StringToIntBenchmark --help for benchmark options

Tests configuration

• gcc 5.4.0 and clang 3.8.0
• arch : x86_64
• cpu : I7-2640M
• gcc flag : -O3
• clang flag : -O3

Tests Results

atoi reference

1. GCC 4.9.2

--------------------------------------------------------
Benchmark                 Time           CPU Iterations
--------------------------------------------------------
BM_fast_atoi/7           34 ns         34 ns   16566159
BM_atoi/7               161 ns        161 ns    4321834
BM_stoi/7               164 ns        164 ns    4242043
BM_sstream/7           2942 ns       2941 ns     239618
BM_lexicalCast/7        225 ns        225 ns    3117588
BM_qiParse/7             42 ns         42 ns   16581565    


2. CLANG 3.5.0

--------------------------------------------------------
Benchmark                 Time           CPU Iterations
--------------------------------------------------------
BM_fast_atoi/7           33 ns         33 ns   17135422
BM_atoi/7               162 ns        162 ns    4318101
BM_stoi/7               161 ns        161 ns    4318646
BM_sstream/7           2742 ns       2742 ns     253361
BM_lexicalCast/7        324 ns        324 ns    2163453
BM_qiParse/7             67 ns         67 ns   10338957 

Conclusion

Whether with Gcc or Clang, the naive function offers the best performance. So use your own atoi function.