user-0 提问: C 语言函数 atof()

回复:
user: user-1
content: 自己实际测试一下比听别人说印象要好得多

user: user-2
content: 如果汉字字母开头会得到0.0 如果是如“1.5xxx”会得到1.5 楼主自己测试下不就知了

user: user-3
content: atof, atoi, _atoi64, atol Convert strings to double (atof), integer (atoi, _atoi64), or long (atol).  double atof( const char *string );  int atoi( const char *string );  __int64 _atoi64( const char *string );  long atol( const char *string );  Routine Required Header Compatibility  atof <math.h> and <stdlib.h> ANSI, Win 95, Win NT  atoi <stdlib.h> ANSI, Win 95, Win NT  _atoi64 <stdlib.h> Win 95, Win NT  atol <stdlib.h> ANSI, Win 95, Win NT    For additional compatibility information, see Compatibility in the Introduction.  Libraries  LIBC.LIB Single thread static library, retail version  LIBCMT.LIB Multithread static library, retail version  MSVCRT.LIB Import library for MSVCRT.DLL, retail version    Return Value  Each function returns the double, int, __int64 or long value produced by interpreting the input characters as a number. The return value is 0 (for atoi and _atoi64), 0L (for atol), or 0.0 (for atof) if the input cannot be converted to a value of that type. The return value is undefined in case of overflow.  Parameter  string  String to be converted  Remarks  These functions convert a character string to a double-precision floating-point value (atof), an integer value (atoi and _atoi64), or a long integer value (atol). The input string is a sequence of characters that can be interpreted as a numerical value of the specified type. The output value is affected by the setting of the LC_NUMERIC category in the current locale. For more information on the LC_NUMERIC category, see setlocale. The longest string size that atof can handle is 100 characters. The function stops reading the input string at the first character that it cannot recognize as part of a number. This character may be the null character ('\0') terminating the string.  The string argument to atof has the following form:  [whitespace] [sign] [digits] [.digits] [ {d | D | e | E }[sign]digits]  A whitespace consists of space and/or tab characters, which are ignored; sign is either plus (+) or minus ( – ); and digits are one or more decimal digits. If no digits appear before the decimal point, at least one must appear after the decimal point. The decimal digits may be followed by an exponent, which consists of an introductory letter ( d, D, e, or E) and an optionally signed decimal integer.  atoi, _atoi64, and atol do not recognize decimal points or exponents. The string argument for these functions has the form:  [whitespace] [sign]digits  where whitespace, sign, and digits are exactly as described above for atof.  Generic-Text Routine Mappings  TCHAR.H Routine  _UNICODE & _MBCS Not Defined _MBCS Defined _UNICODE Defined  _ttoi atoi atoi _wtoi  _ttol atol atol _wtol    Example  /* ATOF.C: This program shows how numbers stored  * as strings can be converted to numeric values  * using the atof, atoi, and atol functions.  */  #include <stdlib.h> #include <stdio.h>  void main( void ) {    char *s; double x; int i; long l;     s = "  -2309.12E-15";    /* Test of atof */    x = atof( s );    printf( "atof test: ASCII string: %s\tfloat:  %e\n", s, x );     s = "7.8912654773d210";  /* Test of atof */    x = atof( s );    printf( "atof test: ASCII string: %s\tfloat:  %e\n", s, x );     s = "  -9885 pigs";      /* Test of atoi */    i = atoi( s );    printf( "atoi test: ASCII string: %s\t\tinteger: %d\n", s, i );     s = "98854 dollars";     /* Test of atol */    l = atol( s );    printf( "atol test: ASCII string: %s\t\tlong: %ld\n", s, l ); }   Output  atof test: ASCII string:   -2309.12E-15   float:  -2.309120e-012 atof test: ASCII string: 7.8912654773d210   float:  7.891265e+210 atoi test: ASCII string:   -9885 pigs      integer: -9885 atol test: ASCII string: 98854 dollars      long: 98854   Data Conversion Routines |  Floating-Point Support Routines |  Locale Routines  See Also   _ecvt, _fcvt, _gcvt, setlocale, strtod, wcstol, strtoul

user: user-4
content: NULL会抛异常 空字符串和汉字得到0