十六度进制负数如何转换为十进制数

[ldkcumt]

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。

[xiaohuh421]

对于strtol函数, 有溢出处理的. strtol的源码中 实际调用的是strtol.c文件中的strtoxl, 在strtoxl的源中有如下代码:

/* 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;

可以明显看到, 如果不是无符号数, 超过了0x7FFFFFFF就强制等于0x7FFFFFFF. 所以你想格式化任意的16进制,有符号无符号. 可以使用strtoul然后再转换成有符号. long iVal = (long)strtoul( "FFFFFC18", NULL, 16 );

[ldkcumt]

xiaohuh421 君 正解。 虽然不太明白，但可以实现。 另外，我写的是32位的MFC应用程序（虽然用的是WIN7 64位操作系统），所以strtoul的第一个参数必须是 "FFFFFC18"， 如果写64位应用程序，则第一个参数是"FFFFFFFFFFFFFC18".

[ldkcumt]

更正一下：关于数据类型 long都是32位的

[赵4老师]

strtol( "FFFFFFFFFFFFFC18", NULL, 16 );

[赵4老师]

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] [{+ | –}] [0 [{ x | 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 | Locale Routines | 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;
}

[mujiok2003]

#include <stdio.h>
int main()
{
  int a = 0;
  sscanf("-1000", "%x", &a);
  printf("%+d",a);
  
  return 0;
}
//-4096