Merge pull request #314 from fastfloat/P2497R0

implementation of p2497

Author: lemire

CMakeLists.txt

@@ -1,4 +1,5 @@
-cmake_minimum_required(VERSION 3.10)
+cmake_minimum_required(VERSION 3.14)
+
 
 project(fast_float VERSION 8.0.2 LANGUAGES CXX)
 set(FASTFLOAT_CXX_STANDARD 11 CACHE STRING "the C++ standard to use for fastfloat")

README.md

@@ -57,6 +57,7 @@ Example:
 ```C++
 #include "fast_float/fast_float.h"
 #include <iostream>
+#include <string>
 
 int main() {
   std::string input = "3.1416 xyz ";
@@ -68,6 +69,25 @@ int main() {
 }
 ```
 
+Though the C++17 standard has you do a comparison with `std::errc()` to check whether the conversion worked, you can avoid it by casting the result to a `bool` like so:
+
+```cpp
+#include "fast_float/fast_float.h"
+#include <iostream>
+#include <string>
+
+int main() {
+  std::string input = "3.1416 xyz ";
+  double result;
+  if(auto answer = fast_float::from_chars(input.data(), input.data() + input.size(), result)) {
+    std::cout << "parsed the number " << result << std::endl;
+    return EXIT_SUCCESS;
+  }
+  std::cerr << "failed to parse " << result << std::endl;
+  return EXIT_FAILURE;
+}
+```
+
 You can parse delimited numbers:
 
 ```C++

include/fast_float/float_common.h

@@ -58,6 +58,11 @@ enum class chars_format : uint64_t {
 template <typename UC> struct from_chars_result_t {
   UC const *ptr;
   std::errc ec;
+
+  // https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2497r0.html
+  constexpr explicit operator bool() const noexcept {
+    return ec == std::errc();
+  }
 };
 
 using from_chars_result = from_chars_result_t<char>;

tests/CMakeLists.txt

@@ -22,12 +22,8 @@ endif()
 
 # FetchContent_MakeAvailable() was only introduced in 3.14
 # https://cmake.org/cmake/help/v3.14/release/3.14.html#modules
-# FetchContent_MakeAvailable(doctest)
 if (NOT SYSTEM_DOCTEST)
-  FetchContent_GetProperties(doctest)
-  if(NOT doctest_POPULATED)
-    FetchContent_MakeAvailable(doctest)
-  endif()
+  FetchContent_MakeAvailable(doctest)
 endif()
 
 add_library(supplemental-data INTERFACE)
@@ -76,7 +72,7 @@ endif()
 if (FASTFLOAT_SUPPLEMENTAL_TESTS)
   target_compile_definitions(basictest PRIVATE FASTFLOAT_SUPPLEMENTAL_TESTS)
 endif()
-
+fast_float_add_cpp_test(p2497)
 fast_float_add_cpp_test(long_test)
 fast_float_add_cpp_test(powersoffive_hardround)
 fast_float_add_cpp_test(string_test)

tests/p2497.cpp

@@ -0,0 +1,16 @@
+#include "fast_float/fast_float.h"
+
+#include <iostream>
+#include <string>
+
+int main() {
+  std::string input = "3.1416 xyz ";
+  double result;
+  if (auto answer = fast_float::from_chars(
+          input.data(), input.data() + input.size(), result)) {
+    std::cout << "parsed the number " << result << std::endl;
+    return EXIT_SUCCESS;
+  }
+  std::cerr << "failed to parse " << result << std::endl;
+  return EXIT_FAILURE;
+}