十六度进制负数如何转换为十进制数
例如：_itoa(-1000,buffer,16);
可以将 －1000转换为 FFFFFC18；
但反过来如何把 FFFFFC18 转换为 －1000呢？
我用 strtol( "FFFFFC18", NULL, 16 );得到是一个很大的正数。
[解决办法]
纠正1楼：
strtol, wcstol
Convert strings to a long-integer value.
long strtol( const char *nptr, char **endptr, int base );
long wcstol( const wchar_t *nptr, wchar_t **endptr, int base );
Routine Required Header Compatibility
strtol <stdlib.h> ANSI, Win 95, Win NT
wcstol <stdlib.h> or <wchar.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
strtol returns the value represented in the string nptr, except when the representation would cause an overflow, in which case it returns LONG_MAX or LONG_MIN. strtol returns 0 if no conversion can be performed. wcstol returns values analogously to strtol. For both functions, errno is set to ERANGE if overflow or underflow occurs.
Parameters
nptr
Null-terminated string to convert
endptr
Pointer to character that stops scan
base
Number base to use
Remarks
The strtol function converts nptr to a long. strtol stops reading the string nptr at the first character it cannot recognize as part of a number. This may be the terminating null character, or it may be the first numeric character greater than or equal to base.
wcstol is a wide-character version of strtol; its nptr argument is a wide-character string. Otherwise these functions behave identically.
Generic-Text Routine Mappings
TCHAR.H Routine _UNICODE & _MBCS Not Defined _MBCS Defined _UNICODE Defined
_tcstol strtol strtol wcstol
The current locale’s LC_NUMERIC category setting determines recognition of the radix character in nptr; for more information, see setlocale. If endptr is not NULL, a pointer to the character that stopped the scan is stored at the location pointed to by endptr. If no conversion can be performed (no valid digits were found or an invalid base was specified), the value of nptr is stored at the location pointed to by endptr.
strtol expects nptr to point to a string of the following form:
[whitespace] [{+
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–}] [0 [{ x
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X }]] [digits]
A whitespace may consist of space and tab characters, which are ignored; digits are one or more decimal digits. The first character that does not fit this form stops the scan. If base is between 2 and 36, then it is used as the base of the number. If base is 0, the initial characters of the string pointed to by nptr are used to determine the base. If the first character is 0 and the second character is not 'x' or 'X', the string is interpreted as an octal integer; otherwise, it is interpreted as a decimal number. If the first character is '0' and the second character is 'x' or 'X', the string is interpreted as a hexadecimal integer. If the first character is '1' through '9', the string is interpreted as a decimal integer. The letters 'a' through 'z' (or 'A' through 'Z') are assigned the values 10 through 35; only letters whose assigned values are less than base are permitted.
Example
/* STRTOD.C: This program uses strtod to convert a
* string to a double-precision value; strtol to
* convert a string to long integer values; and strtoul
* to convert a string to unsigned long-integer values.
*/
#include <stdlib.h>
#include <stdio.h>
void main( void )
{
char *string, *stopstring;
double x;
long l;
int base;
unsigned long ul;
string = "3.1415926This stopped it";
x = strtod( string, &stopstring );
printf( "string = %s\n", string );
printf(" strtod = %f\n", x );
printf(" Stopped scan at: %s\n\n", stopstring );
string = "-10110134932This stopped it";
l = strtol( string, &stopstring, 10 );
printf( "string = %s", string );
printf(" strtol = %ld", l );
printf(" Stopped scan at: %s", stopstring );
string = "10110134932";
printf( "string = %s\n", string );
/* Convert string using base 2, 4, and 8: */
for( base = 2; base <= 8; base *= 2 )
{
/* Convert the string: */
ul = strtoul( string, &stopstring, base );
printf( " strtol = %ld (base %d)\n", ul, base );
printf( " Stopped scan at: %s\n", stopstring );
}
}
Output
string = 3.1415926This stopped it
strtod = 3.141593
Stopped scan at: This stopped it
string = -10110134932This stopped it strtol = -2147483647 Stopped scan at: This stopped itstring = 10110134932
strtol = 45 (base 2)
Stopped scan at: 34932
strtol = 4423 (base 4)
Stopped scan at: 4932
strtol = 2134108 (base 8)
Stopped scan at: 932
Data Conversion Routines
[解决办法]
Locale Routines
[解决办法]
strtod Functions Overview
See Also strtod, strtoul, atof, localeconv, setlocale
#include <stdio.h>
#include <stdlib.h>
int main() {
long l;
char *e;
l=strtol("FFFFFC18", &e, 16 );
printf("%ld\n",l);//2147483647
sscanf("FFFFFC18","%X",&l);
printf("%ld\n",l);//-1000
return 0;
}
/* overflow or signed overflow occurred */
errno = ERANGE;
if ( flags & FL_UNSIGNED )
number = ULONG_MAX;
else if ( flags & FL_NEG )
number = (unsigned long)(-LONG_MIN);
else
number = LONG_MAX;
