STRTOD(3) | Library Functions Manual | STRTOD(3) |
double
strtod(const char * restrict nptr, char ** restrict endptr);
float
strtof(const char * restrict nptr, char ** restrict endptr);
long double
strtold(const char * restrict nptr, char ** restrict endptr);
The strtof() function converts the initial portion of the string pointed to by nptr to float representation.
The strtold() function converts the initial portion of the string pointed to by nptr to long double representation.
The expected form of the string is an optional plus (‘+’) or minus sign (‘-’) followed by one of the following:
INF
or INFINITY
, ignoring case.NAN
or NAN(n-char-sequence-opt)
, ignoring case. This implementation currently does not interpret such a sequence.Leading white-space characters in the string (as defined by the isspace(3) function) are skipped.
A character sequence INF
or INFINITY
is converted to infinity, if supported, else to the largest finite floating-point number representable on the machine (i.e., VAX).
A character sequence NAN
or NAN(n-char-sequence-opt)
is converted to a quiet NaN, if supported, else remains unrecognized (i.e., VAX).
If endptr is not NULL, a pointer to the character after the last character used in the conversion is stored in the location referenced by endptr.
If no conversion is performed, zero is returned and the value of nptr is stored in the location referenced by endptr.
If the correct value is too large in magnitude to be represented (‘overflow’), plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the return type and sign of the value), and ERANGE is stored in errno.
If the correct value is too small in magnitude to be represented normally with full precision (‘underflow’), the closest subnormal value, or zero, is returned, and ERANGE is stored in errno.
To check for syntax errors, callers must also check whether endptr was updated to reflect the true end of the string in order to determine whether the full string was consumed or whether there were additional erroneous characters in it.
char *end; double d; ... errno = 0; d = strtod(s, &end); if (end == s) errx(EXIT_FAILURE, "invalid syntax"); if (end[0] != '\0') errx(EXIT_FAILURE, "trailing garbage"); if (errno) { assert(errno == ERANGE); assert(isinf(d) || d == 0 || fpclassify(d) == FP_SUBNORMAL); warnx("%s", isinf(d) ? "overflow" : "underflow"); } /* d is the best floating-point approximation to the number in s */
November 4, 2016 | NetBSD 7.2 |