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
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
git clone https://github.com/benoit-bst/stringToIntBenchmark
cd StringtoIntBenchmark
git submodule update --init
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
for each function, we test 7 sizes of string (1->7)
./StringToIntBenchmark --benchmark_out=results --benchmark_out_format=csv
./StringToIntBenchmark --help for benchmark options
- gcc 5.4.0 and clang 3.8.0
- arch : x86_64
- cpu : I7-2640M
- gcc flag : -O3
- clang flag : -O3
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
Whether with Gcc or Clang, the naive function offers the best performance. So use your own atoi function.
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