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Fix wording #323

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Fix wording #323

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24 changes: 14 additions & 10 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -58,40 +58,44 @@ Example:
#include "fast_float/fast_float.h"
#include <iostream>
#include <string>
#include <system_error>

int main() {
std::string input = "3.1416 xyz ";
const std::string input = "3.1416 xyz ";
double result;
auto answer = fast_float::from_chars(input.data(), input.data() + input.size(), result);
if (answer.ec != std::errc()) { std::cerr << "parsing failure\n"; return EXIT_FAILURE; }
std::cout << "parsed the number " << result << std::endl;
if (answer.ec != std::errc()) {
std::cerr << "parsing failure\n";
return EXIT_FAILURE;
}
std::cout << "parsed the number " << result << '\n';
return EXIT_SUCCESS;
}
```

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:
You can simplify the conversion success check by casting the result of `from_chars` to `bool`, as shown below:
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The original text sounds clunky but it makes an important point that this edit removes. The C++17 standard does not include this cast to bool. It's important for users to know that it is a fast_float extension.

The cast to bool only became standard in C++26. https://en.cppreference.com/w/cpp/utility/from_chars_result.html

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Yes, there is still room for improvement. The point is that I did not understand the actual purpose of the original statement. Neither does it mention C++26.

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The original wording is valid English, but how about:

In C++17, to check whether the conversion succeeded, you must compare the ec member to std::errc(). As an extension, fast float supports the C++26 feature that allows you to cast the result to bool, like so:

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Yes, that's easier to comprehend for non-native English speakers. So what about C++20 then?

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Everything else in that document talks about C++17 from_chars, and I think it should be obvious that unless stated otherwise, the same API is present in C++20 and C++23.

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@thbeu thbeu Sep 21, 2025 •
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What about this?

Whereas before C++26 std::from_chars needs to be explicitily compared with std::errc() to check for conversion success, fast_float::from_chars simplifies the check as shown below:

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from_chars is a function, you don't compare it to std::errc(), and you don't even compare its return value to std::errc(), so I don't think that's good.

"to check for a successful conversion" would be better than "to check for conversion success".

I don't think there's a problem with simply referring to C++17 as the standard that defined the from_chars feature, but if you insist, then maybe:

Prior to C++26, checking for a successful std::from_chars conversion requires comparing the from_chars_result::ec member to std::errc(). As an extension fast_float::from_chars supports the improved C++26 API that allows checking the result by converting it to bool, like so:


```cpp
```C++
#include "fast_float/fast_float.h"
#include <iostream>
#include <string>

int main() {
std::string input = "3.1416 xyz ";
const 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;
if (auto answer = fast_float::from_chars(input.data(), input.data() + input.size(), result)) {
std::cout << "parsed the number " << result << '\n';
return EXIT_SUCCESS;
}
std::cerr << "failed to parse " << result << std::endl;
std::cerr << "parsing failure\n";
return EXIT_FAILURE;
}
```

You can parse delimited numbers:

```C++
std::string input = "234532.3426362,7869234.9823,324562.645";
const std::string input = "234532.3426362,7869234.9823,324562.645";
double result;
auto answer = fast_float::from_chars(input.data(), input.data() + input.size(), result);
if (answer.ec != std::errc()) {
Expand Down