What Are The Elementary String Conversions That Come With C++ 17?

In addition to many beneficial features of C++ 17, there are elementary string conversions introduced in that specification. The std::to_chars() and std::from_chars() are defined in <charconv> header to do conversions between numeric values to strings or strings to numeric values without considering locale-specific conversions. In this post, we explain the std::to_chars() and std::from_chars() that come with C++17.

What Are The Elementary String Conversions That Come With C++ 17 ?

What is std::to_chars()?

The std::to_chars() is defined in header and is used to convert numeric values into a character string within the given valid range.

The std::to_chars() is designed to copy the numeric value into a string buffer, with a given specific format, with the only overhead of making sure that the buffer is big enough. You don’t need to consider locale-specific conversions.

Here is the syntax of std::to_chars in C++ 17.

Here is a simple example.

In floating point number conversions, std::chars_format types can be used (i.e. std::chars_format::fixed, std::chars_format::scientific, std::chars_format::general,…)

What is std::from_chars()?

The std::from_chars() is defined in the header and used to convert the string data in a given range to a value (string to int, string to float operations) if no string characters match the pattern or if the obtained value is not representable in a given type of value, then the value has remains unchanged.

The std::from_chars() is a lightweight parser that does not need to create dynamic allocation, and you don’t need to consider locale-specific conversions.

Here is the syntax of std::from_chars in C++ 17.

Here is a simple example.

Is there a full example to elementary string conversions that comes with C++ 17?

Here is a full example about std::to_chars() and std::from_chars() in C++ 17.

Here is the output.

Note that here ec is error check parameter and can be used to check error by if( ec = std::erc() ) { ... } or other error check members can be used, i.e. if (ec == std::errc::invalid_argument) { ... }. The benefits of these conversion methods are compatible with the locale-specific conversions.

For more details about this feature in C++17 standard, please see these papers; P0067R5, P0682R1^DR

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