strtof, strtod, strtold
Defined in header <stdlib.h>
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(since C99) | |
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(until C99) | |
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(since C99) | |
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(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) |
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