std::strtof...td::strtold(3)

✨ std::strtof...td::strtold(3) ✨

okay so bestie, welcome to the std::strtof...td::strtold(3) page from the C++ Standard Libary 💅. This is the one where we parse floating-point numbers out of byte strings, and it’s honestly kind of iconic.

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🌸 NAME 🌸

• std::strtof,std::strtod,std::strtold — std::strtof,std::strtod,std::strtold

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🦋 Synopsis 🦋

Defined in header <cstdlib>

float       strtof( const char* str, char** str_end );   (since C++11)
double      strtod( const char* str, char** str_end );
long double strtold( const char* str, char** str_end );  (since C++11)

Interprets a floating point value in a byte string pointed to by str.

Function discards any whitespace characters (as determined by std::isspace) until first non-whitespace character is found. Then it takes as many characters as possible to form a valid floating-point representation and converts them to a floating-point value. The valid floating-point value can be one of the following:

• decimal floating-point expression. It consists of the following parts:
  • (optional) plus or minus sign
  • nonempty sequence of decimal digits optionally containing decimal-point character (as determined by the current C locale) (defines significand)
  • (optional) e or E followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent to base 10)
• hexadecimal floating-point expression. It consists of the following parts:
  • (optional) plus or minus sign
  • 0x or 0X
  • nonempty sequence of hexadecimal digits optionally containing a decimal-point character (as determined by the current C locale) (defines significand)
  • (optional) p or P followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent to base 2) (since C++11)
• infinity expression. It consists of the following parts:
  • (optional) plus or minus sign
  • INF or INFINITY ignoring case
• not-a-number expression. It consists of the following parts:
  • (optional) plus or minus sign
  • NAN or NAN(char_sequence) ignoring case of the NAN part. char_sequence can only contain digits, Latin letters, and underscores. The result is a quiet NaN floating-point value.
• any other expression that may be accepted by the currently installed C locale

The functions sets the pointer pointed to by str_end to point to the character past the last character interpreted. If str_end is a null pointer, it is ignored.

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💅 Parameters 💅

• str — pointer to the null-terminated byte string to be interpreted
• str_end — pointer to a pointer to character.

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🔥 Return value 🔥

Floating point value corresponding to the contents of str on success. If the converted value falls out of range of corresponding return type, range error occurs and HUGE_VAL, HUGE_VALF or HUGE_VALL is returned. If no conversion can be performed, 0 is returned and *str_end is set to str.

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🎀 Example 🎀

// Run this code
#include <cerrno>
#include <clocale>
#include <cstdlib>
#include <iostream>
#include <string>

int main()
{
    const char* p = "111.11 -2.22 0X1.BC70A3D70A3D7P+6 -Inf 1.18973e+4932zzz";
    char* end{};
    std::cout << "Parsing \"" << p << "\":\n";
    errno = 0;
    for (double f = std::strtod(p, &end); p != end; f = std::strtod(p, &end))
    {
        std::cout << "  '" << std::string(p, end - p) << "' -> ";
        p = end;
        if (errno == ERANGE)
        {
            std::cout << "range error, got ";
            errno = 0;
        }
        std::cout << f << '\n';
    }

    if (std::setlocale(LC_NUMERIC, "de_DE.utf8"))
    {
        std::cout << "With de_DE.utf8 locale:\n";
        std::cout << "  '123.45' -> " << std::strtod("123.45", 0) << '\n';
        std::cout << "  '123,45' -> " << std::strtod("123,45", 0) << '\n';
    }
}

💀 Possible output 💀

Parsing "111.11 -2.22 0X1.BC70A3D70A3D7P+6 -Inf 1.18973e+4932zzz":
  '111.11' -> 111.11
  ' -2.22' -> -2.22
  ' 0X1.BC70A3D70A3D7P+6' -> 111.11
  ' -Inf' -> -inf
  ' 1.18973e+4932' -> range error, got inf
With de_DE.utf8 locale:
  '123.45' -> 123
  '123,45' -> 123.45

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🌈 See also 🌈

• atof — converts a byte string to a floating point value (function)
• wcstof — converts a wide string to a floating-point value
• wcstod — (function)
• wcstold
• from_chars (C++17) — converts a character sequence to an integer or floating-point value (function)
• C documentation for strtof, strtod, strtold

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xoxo, your C++ bestie 💖 — source: http://cppreference.com, version: 2024.06.10, page: std::strtof...td::strtold(3) ✨