strtof, strtod, strtold
Defined in header <stdlib.h>
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float strtof( const char *restrict str, char **restrict str_end ); |
(since C99) | |
double strtod( const char *str, char **str_end ); |
(until C99) | |
double strtod( const char *restrict str, char **restrict str_end ); |
(since C99) | |
long double strtold( const char *restrict str, char **restrict str_end ); |
(since C99) | |
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
orE
followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent)
- binary floating-point expression. It consists of the following parts:
- (optional) plus or minus sign
-
0x
or0X
- nonempty sequence of hexadecimal digits optionally containing a decimal-point character (as determined by the current C locale) (defines significand)
- (optional)
p
orP
followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent)
- infinity expression. It consists of the following parts:
- (optional) plus or minus sign
-
INF
orINFINITY
ignoring case
- not-a-number expression. It consists of the following parts:
- (optional) plus or minus sign
-
NAN
orNAN(
char_sequence)
ignoring case of theNAN
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 NULL, it is ignored.
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 <stdio.h> #include <errno.h> #include <stdlib.h> int main(void) { // parsing with error handling const char *p = "111.11 -2.22 Nan nan(2) inF 0X1.BC70A3D70A3D7P+6 1.18973e+4932zzz"; printf("Parsing '%s':\n", p); char *end; for (double f = strtod(p, &end); p != end; f = strtod(p, &end)) { printf("'%.*s' -> ", (int)(end-p), p); p = end; if (errno == ERANGE){ printf("range error, got "); errno = 0; } printf("%f\n", f); } // parsing without error handling printf("\" -0.0000000123junk\" --> %g\n", strtod(" -0.0000000123junk", NULL)); printf("\"junk\" --> %g\n", strtod("junk", NULL)); }
Possible output:
Parsing '111.11 -2.22 Nan inF 0X1.BC70A3D70A3D7P+6 1.18973e+4932zzz': '111.11' -> 111.110000 ' -2.22' -> -2.220000 ' Nan' -> nan ' nan(2)' -> nan ' inF' -> inf ' 0X1.BC70A3D70A3D7P+6' -> 111.110000 ' 1.18973e+4932' -> range error, got inf " -0.0000000123junk" --> -1.23e-08 "junk" --> 0
References
- C11 standard (ISO/IEC 9899:2011):
- 7.22.1.3 The strtod, strtof, and strtold functions (p: 342-344)
- C99 standard (ISO/IEC 9899:1999):
- 7.20.1.3 The strtod, strtof, and strtold functions (p: 308-310)
- C89/C90 standard (ISO/IEC 9899:1990):
- 4.10.1.4 The strtod function
See also
converts a byte string to a floating-point value (function) | |
(C99)(C95)(C99) |
converts a wide string to a floating-point value (function) |