std::strtof, std::strtod, std::strtold

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)

• 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.

[edit] Parameters

[edit] 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.

[edit] Example

#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';
 }
}

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

[edit] See also

• In other languages

• Deutsch
• Español
• Français
• Italiano
• 日本語
• Português
• Русский
• 中文