format/formatperf.cpp

The following code example is taken from the book
C++20 - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2021
The code is licensed under a Creative Commons Attribution 4.0 International License.

---

// raw code

#include <iostream>
#include <string>
#include <sstream>
#include <charconv>
#include <chrono>
#ifdef __cpp_lib_format
#include <format>
#else
#include <fmt/format.h>
#endif

static void checkSPrintf(int num) {
  for (int idx = 0; idx < num; ++idx) {
    int i = 42;
    double d = 7.7;
    char buf[100] = {'?', '?', '?', '?', '?', '?', '?', '?', '?', '?', '?', '?', '?'};
    sprintf(buf, "%d %f", i, d);
    if (num == 1) {
      std::cout << buf << '\n';
      return;
    }
  }
}

static void checkOStringStream(int num) {
  for (int idx = 0; idx < num; ++idx) {
    int i = 42;
    double d = 7.7;
    std::ostringstream os;
    os << i << ' ' << d;
    if (num == 1) {
      std::cout << os.str() << '\n';
      return;
    }
  }
}

static void checkToString(int num) {
  for (int idx = 0; idx < num; ++idx) {
    int i = 42;
    double d = 7.7;
    std::string s = std::to_string(i) + ' ' + std::to_string(d);
    if (num == 1) {
      std::cout << s << '\n';
      return;
    }
  }
}

static void checkToChars(int num) {
  for (int idx = 0; idx < num; ++idx) {
    int i = 42;
    double d = 7.7;
    char buf[100] = {'?', '?', '?', '?', '?', '?', '?', '?', '?', '?', '?', '?', '?'};
    std::to_chars_result res = std::to_chars(buf, buf+9, i);
    *res.ptr = ' ';
    res = std::to_chars(res.ptr+1, res.ptr+10, d);
    *res.ptr = '\0';
    if (num == 1) {
      std::cout << buf << '\n';
      return;
    }
  }
}

static void checkFormat(int num) {
  for (int idx = 0; idx < num; ++idx) {
    int i = 42;
    double d = 7.7;
#ifdef __cpp_lib_format
    auto s = std::format("{} {}", i, d);
#else
    auto s = fmt::v8::format("{} {}", i, d);
#endif
    if (num == 1) {
      std::cout << s << '\n';
      return;
    }
  }
}

static void checkFormatTo(int num) {
  for (int idx = 0; idx < num; ++idx) {
    int i = 42;
    double d = 7.7;
    char buf[100] = {'?', '?', '?', '?', '?', '?', '?', '?', '?', '?', '?', '?', '?'};
#ifdef __cpp_lib_format
    auto ret = std::format_to_n(buf, 99, "{} {}", i, d);
    *(ret.out) = '\0';
#else
    auto ret = fmt::v8::format_to(buf, "{} {}", i, d);
    *ret = '\0';
#endif
    if (num == 1) {
      std::cout << buf << '\n';
      return;
    }
  }
}


template<typename T>
void measure(std::string s, T func)
{
  auto t0 = std::chrono::steady_clock::now();
  func(1000);    // measure
  auto t1 = std::chrono::steady_clock::now();
  std::chrono::duration<double, std::milli> diff{t1 - t0};
  std::cout << s << ": " << diff.count() << "ms\n ";
  func(1);       // show output

}

int main()
{
  measure("sprintf()    ", checkSPrintf);
  measure("ostringstream", checkOStringStream);
  measure("to_string()  ", checkToString);
  measure("to_chars()   ", checkToChars);
  measure("format()     ", checkFormat);
  measure("format_to()  ", checkFormatTo);
}