Difference between revisions of "cpp/string/byte/strtof"
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Revision as of 22:25, 31 May 2013
| 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)
eorEfollowed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent to base 10)
|
(since C++11) |
- 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 NULL, it is ignored.
Contents |
Parameters
| str | - | pointer to the null-terminated byte string to be interpreted |
| str_end | - | pointer to a pointer to character. |
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.
Example
#include <cstdlib> #include <iostream> int main() { std::cout << std::strtod("0.0000000123", nullptr) << "\n"; // the second arg of strto* is non-const. We must copy the string char src[] = "0.012 15e16 -0x1afp-2 inF Nan"; char* c = src; std::cout << std::strtod(c, &c) << "\n"; std::cout << std::strtod(c, &c) << "\n"; std::cout << std::strtod(c, &c) << "\n"; std::cout << std::strtod(c, &c) << "\n"; std::cout << std::strtod(c, &c) << "\n"; }
Output:
1.23e-08 0.012 1.5e+17 -107.75 inf nan
See also
| converts a byte string to a floating point value (function) | |
| C documentation for strtof, strtod, strtold
| |
