/* * strtod.c -- * * Source code for the "strtod" library procedure. * * Copyright (c) 1988-1993 The Regents of the University of California. * Copyright (c) 1994 Sun Microsystems, Inc. * * See the file "license.terms" for information on usage and redistribution * of this file, and for a DISCLAIMER OF ALL WARRANTIES. * * RCS: @(#) $Id: strtod.c,v 1.6 2002/02/25 14:26:12 dgp Exp $ */#include "tclInt.h" #include "tclPort.h" #include <ctype.h>#ifndef TRUE #define TRUE 1 #define FALSE 0 #endif #ifndef NULL #define NULL 0 #endifstatic int maxExponent = 511; /* Largest possible base 10 exponent. Any * exponent larger than this will already * produce underflow or overflow, so there's * no need to worry about additional digits. */ static double powersOf10[] = { /* Table giving binary powers of 10. Entry */ 10., /* is 10^2^i. Used to convert decimal */ 100., /* exponents into floating-point numbers. */ 1.0e4, 1.0e8, 1.0e16, 1.0e32, 1.0e64, 1.0e128, 1.0e256 };
/* *---------------------------------------------------------------------- * * strtod -- * * This procedure converts a floating-point number from an ASCII * decimal representation to internal double-precision format. * * Results: * The return value is the double-precision floating-point * representation of the characters in string. If endPtr isn't * NULL, then *endPtr is filled in with the address of the * next character after the last one that was part of the * floating-point number. * * Side effects: * None. * *---------------------------------------------------------------------- */double strtod(string, endPtr) CONST char *string; /* A decimal ASCII floating-point number, * optionally preceded by white space. * Must have form "-I.FE-X", where I is the * integer part of the mantissa, F is the * fractional part of the mantissa, and X * is the exponent. Either of the signs * may be "+", "-", or omitted. Either I * or F may be omitted, or both. The decimal * point isn't necessary unless F is present. * The "E" may actually be an "e". E and X * may both be omitted (but not just one). */ char **endPtr; /* If non-NULL, store terminating character's * address here. */ { int sign, expSign = FALSE; double fraction, dblExp, *d; register CONST char *p; register int c; int exp = 0; /* Exponent read from "EX" field. */ int fracExp = 0; /* Exponent that derives from the fractional * part. Under normal circumstatnces, it is * the negative of the number of digits in F. * However, if I is very long, the last digits * of I get dropped (otherwise a long I with a * large negative exponent could cause an * unnecessary overflow on I alone). In this * case, fracExp is incremented one for each * dropped digit. */ int mantSize; /* Number of digits in mantissa. */ int decPt; /* Number of mantissa digits BEFORE decimal * point. */ CONST char *pExp; /* Temporarily holds location of exponent * in string. */ /* * Strip off leading blanks and check for a sign. */ p = string; while (isspace(UCHAR(*p))) { p += 1; } if (*p == '-') { sign = TRUE; p += 1; } else { if (*p == '+') { p += 1; } sign = FALSE; } /* * Count the number of digits in the mantissa (including the decimal * point), and also locate the decimal point. */ decPt = -1; for (mantSize = 0; ; mantSize += 1) { c = *p; if (!isdigit(c)) { if ((c != '.') || (decPt >= 0)) { break; } decPt = mantSize; } p += 1; } /* * Now suck up the digits in the mantissa. Use two integers to * collect 9 digits each (this is faster than using floating-point). * If the mantissa has more than 18 digits, ignore the extras, since * they can't affect the value anyway. */
pExp = p; p -= mantSize; if (decPt < 0) { decPt = mantSize; } else { mantSize -= 1; /* One of the digits was the point. */ } if (mantSize > 18) { fracExp = decPt - 18; mantSize = 18; } else { fracExp = decPt - mantSize; } if (mantSize == 0) { fraction = 0.0; p = string; goto done; } else { int frac1, frac2; frac1 = 0; for ( ; mantSize > 9; mantSize -= 1) { c = *p; p += 1; if (c == '.') { c = *p; p += 1; } frac1 = 10*frac1 + (c - '0'); } frac2 = 0; for (; mantSize > 0; mantSize -= 1) { c = *p; p += 1; if (c == '.') { c = *p; p += 1; } frac2 = 10*frac2 + (c - '0'); } fraction = (1.0e9 * frac1) + frac2; } /* * Skim off the exponent. */ p = pExp; if ((*p == 'E') || (*p == 'e')) { p += 1; if (*p == '-') { expSign = TRUE; p += 1; } else { if (*p == '+') { p += 1; } expSign = FALSE; } if (!isdigit(UCHAR(*p))) { p = pExp; goto done; } while (isdigit(UCHAR(*p))) { exp = exp * 10 + (*p - '0'); p += 1; } } if (expSign) { exp = fracExp - exp; } else { exp = fracExp + exp; } /* * Generate a floating-point number that represents the exponent. * Do this by processing the exponent one bit at a time to combine * many powers of 2 of 10. Then combine the exponent with the * fraction. */
* strtod.c --
*
* Source code for the "strtod" library procedure.
*
* Copyright (c) 1988-1993 The Regents of the University of California.
* Copyright (c) 1994 Sun Microsystems, Inc.
*
* See the file "license.terms" for information on usage and redistribution
* of this file, and for a DISCLAIMER OF ALL WARRANTIES.
*
* RCS: @(#) $Id: strtod.c,v 1.6 2002/02/25 14:26:12 dgp Exp $
*/#include "tclInt.h"
#include "tclPort.h"
#include <ctype.h>#ifndef TRUE
#define TRUE 1
#define FALSE 0
#endif
#ifndef NULL
#define NULL 0
#endifstatic int maxExponent = 511; /* Largest possible base 10 exponent. Any
* exponent larger than this will already
* produce underflow or overflow, so there's
* no need to worry about additional digits.
*/
static double powersOf10[] = { /* Table giving binary powers of 10. Entry */
10., /* is 10^2^i. Used to convert decimal */
100., /* exponents into floating-point numbers. */
1.0e4,
1.0e8,
1.0e16,
1.0e32,
1.0e64,
1.0e128,
1.0e256
};
/*
*----------------------------------------------------------------------
*
* strtod --
*
* This procedure converts a floating-point number from an ASCII
* decimal representation to internal double-precision format.
*
* Results:
* The return value is the double-precision floating-point
* representation of the characters in string. If endPtr isn't
* NULL, then *endPtr is filled in with the address of the
* next character after the last one that was part of the
* floating-point number.
*
* Side effects:
* None.
*
*----------------------------------------------------------------------
*/double
strtod(string, endPtr)
CONST char *string; /* A decimal ASCII floating-point number,
* optionally preceded by white space.
* Must have form "-I.FE-X", where I is the
* integer part of the mantissa, F is the
* fractional part of the mantissa, and X
* is the exponent. Either of the signs
* may be "+", "-", or omitted. Either I
* or F may be omitted, or both. The decimal
* point isn't necessary unless F is present.
* The "E" may actually be an "e". E and X
* may both be omitted (but not just one).
*/
char **endPtr; /* If non-NULL, store terminating character's
* address here. */
{
int sign, expSign = FALSE;
double fraction, dblExp, *d;
register CONST char *p;
register int c;
int exp = 0; /* Exponent read from "EX" field. */
int fracExp = 0; /* Exponent that derives from the fractional
* part. Under normal circumstatnces, it is
* the negative of the number of digits in F.
* However, if I is very long, the last digits
* of I get dropped (otherwise a long I with a
* large negative exponent could cause an
* unnecessary overflow on I alone). In this
* case, fracExp is incremented one for each
* dropped digit. */
int mantSize; /* Number of digits in mantissa. */
int decPt; /* Number of mantissa digits BEFORE decimal
* point. */
CONST char *pExp; /* Temporarily holds location of exponent
* in string. */ /*
* Strip off leading blanks and check for a sign.
*/ p = string;
while (isspace(UCHAR(*p))) {
p += 1;
}
if (*p == '-') {
sign = TRUE;
p += 1;
} else {
if (*p == '+') {
p += 1;
}
sign = FALSE;
} /*
* Count the number of digits in the mantissa (including the decimal
* point), and also locate the decimal point.
*/ decPt = -1;
for (mantSize = 0; ; mantSize += 1)
{
c = *p;
if (!isdigit(c)) {
if ((c != '.') || (decPt >= 0)) {
break;
}
decPt = mantSize;
}
p += 1;
} /*
* Now suck up the digits in the mantissa. Use two integers to
* collect 9 digits each (this is faster than using floating-point).
* If the mantissa has more than 18 digits, ignore the extras, since
* they can't affect the value anyway.
*/
pExp = p;
p -= mantSize;
if (decPt < 0) {
decPt = mantSize;
} else {
mantSize -= 1; /* One of the digits was the point. */
}
if (mantSize > 18) {
fracExp = decPt - 18;
mantSize = 18;
} else {
fracExp = decPt - mantSize;
}
if (mantSize == 0) {
fraction = 0.0;
p = string;
goto done;
} else {
int frac1, frac2;
frac1 = 0;
for ( ; mantSize > 9; mantSize -= 1)
{
c = *p;
p += 1;
if (c == '.') {
c = *p;
p += 1;
}
frac1 = 10*frac1 + (c - '0');
}
frac2 = 0;
for (; mantSize > 0; mantSize -= 1)
{
c = *p;
p += 1;
if (c == '.') {
c = *p;
p += 1;
}
frac2 = 10*frac2 + (c - '0');
}
fraction = (1.0e9 * frac1) + frac2;
} /*
* Skim off the exponent.
*/ p = pExp;
if ((*p == 'E') || (*p == 'e')) {
p += 1;
if (*p == '-') {
expSign = TRUE;
p += 1;
} else {
if (*p == '+') {
p += 1;
}
expSign = FALSE;
}
if (!isdigit(UCHAR(*p))) {
p = pExp;
goto done;
}
while (isdigit(UCHAR(*p))) {
exp = exp * 10 + (*p - '0');
p += 1;
}
}
if (expSign) {
exp = fracExp - exp;
} else {
exp = fracExp + exp;
} /*
* Generate a floating-point number that represents the exponent.
* Do this by processing the exponent one bit at a time to combine
* many powers of 2 of 10. Then combine the exponent with the
* fraction.
*/
if (exp < 0) {
expSign = TRUE;
exp = -exp;
} else {
expSign = FALSE;
}
if (exp > maxExponent) {
exp = maxExponent;
errno = ERANGE;
}
dblExp = 1.0;
for (d = powersOf10; exp != 0; exp >>= 1, d += 1) {
if (exp & 01) {
dblExp *= *d;
}
}
if (expSign) {
fraction /= dblExp;
} else {
fraction *= dblExp;
}done:
if (endPtr != NULL) {
*endPtr = (char *) p;
} if (sign) {
return -fraction;
}
return fraction;
}
http://tcl.apache.org/sources/tcl/compat/strtod.c.html
if (!isdigit(UCHAR(*p))) 这句看的不是太懂。
你能帮忙解释一下吗？
字符串str="123"其实就相当于是一个数组char str[4],其中str[0]='1',str[1]='2',str[2]='3',str[3]='\0',在CString中,可以用GetAt取到每个字符的Ascii码,可以从后向前取,这样第1次就是个位,即10^0,第2次就是10^1,以此类推,再将Ascii转化位int就可以了,如果还不懂就留下个email,我发给你代码