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


   #include <stdlib.h>

   double strtod(const char *nptr, char **endptr);
   float strtof(const char *nptr, char **endptr);
   long double strtold(const char *nptr, char **endptr);

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

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


   The  strtod(),  strtof(),  and  strtold() functions convert the initial
   portion of the string pointed to by nptr to  double,  float,  and  long
   double 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 decimal number 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  hexadecimal number 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 NOTES).


   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,  HUGE_VALL)  is  returned  (according  to  the  sign of the
   value), and ERANGE is stored in errno.   If  the  correct  value  would
   cause underflow, zero is returned and ERANGE is stored in errno.


   ERANGE Overflow or underflow occurred.


   For   an   explanation   of   the  terms  used  in  this  section,  see

   │InterfaceAttributeValue          │
   │strtod(), strtof(), strtold() │ Thread safety │ MT-Safe locale │


   POSIX.1-2001, POSIX.1-2008, C99.

   strtod() was also described in C89.


   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.

   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.


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


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


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   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at


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