strtod, strtof, strtold - convert ASCII string to floating-point number

       For an explanation of the terms used in this section, see attributes(7).
       ┌──────────────────────────────────────────────────────────────────────┬───────────────┬────────────────┐
       │ Interface                                                            │ Attribute     │ Value          │
       ├──────────────────────────────────────────────────────────────────────┼───────────────┼────────────────┤
       │ strtod(), strtof(), strtold()                                        │ Thread safety │ MT-Safe locale │
       └──────────────────────────────────────────────────────────────────────┴───────────────┴────────────────┘

       Since 0 can legitimately be returned on both success and failure, the calling program should set errno to
       0 before the call, and then determine if an error occurred by checking whether errno has a nonzero  value
       after the call.

       The  strtod(),  strtof(), and strtold() functions convert the initial portion of the string pointed to by
       nptr to double, float, and longdouble representation, respectively.

       The expected form of the (initial portion of the) string is optional leading white space as recognized by
       isspace(3), an optional plus ('+') or minus sign ('-') and then either (i) a decimal number,  or  (ii)  a
       hexadecimal number, or (iii) an infinity, or (iv) a NAN (not-a-number).

       A  decimalnumber consists of a nonempty sequence of decimal digits possibly containing a radix character
       (decimal point, locale-dependent, usually '.'), optionally followed by a  decimal  exponent.   A  decimal
       exponent  consists  of  an 'E' or 'e', followed by an optional plus or minus sign, followed by a nonempty
       sequence of decimal digits, and indicates multiplication by a power of 10.

       A hexadecimalnumber consists of a "0x" or "0X" followed by a nonempty  sequence  of  hexadecimal  digits
       possibly  containing  a  radix  character,  optionally  followed by a binary exponent.  A binary exponent
       consists of a 'P' or 'p', followed by an optional plus or minus sign, followed by a nonempty sequence  of
       decimal digits, and indicates multiplication by a power of 2.  At least one of radix character and binary
       exponent must be present.

       An infinity is either "INF" or "INFINITY", disregarding case.

       A  NAN  is  "NAN"  (disregarding  case) optionally followed by a string, (n-char-sequence), where n-char-sequence specifies in an implementation-dependent way the type of NAN (see VERSIONS).

ERANGE Overflow or underflow occurred.

       See  the  example on the strtol(3) manual page; the use of the functions described in this manual page is
       similar.

strtod()
              C89, POSIX.1-2001.

       strtof()
       strtold()
              C99, POSIX.1-2001.

       Standard C library (libc, -lc)

       strtod, strtof, strtold - convert ASCII string to floating-point number

       These functions return the converted value, if any.

       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 (unless endptr is null) the value of nptr is stored
       in the location referenced by endptr.

       If the correct value would cause 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 would cause underflow, a value with magnitude no larger than DBL_MIN, FLT_MIN, or
       LDBL_MIN is returned and ERANGE is stored in errno.

atof(3), atoi(3), atol(3), nan(3), nanf(3), nanl(3), strfromd(3), strtol(3), strtoul(3)

Linux man-pages 6.9.1                              2024-06-16                                          strtod(3)

       C11, POSIX.1-2008.

#include<stdlib.h>doublestrtod(constchar*restrictnptr,char**_Nullablerestrictendptr);floatstrtof(constchar*restrictnptr,char**_Nullablerestrictendptr);longdoublestrtold(constchar*restrictnptr,char**_Nullablerestrictendptr);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       strtof(), strtold():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

       In the glibc implementation, the n-char-sequence that optionally  follows  "NAN"  is  interpreted  as  an
       integer  number  (with an optional '0' or '0x' prefix to select base 8 or 16) that is to be placed in the
       mantissa component of the returned value.