# Category : C Source Code

Archive : ECSTR.ZIP

Filename : STR2INT.C

Author : Richard A. O'Keefe

Updated: 27 April 1984

Defines: str2int(), atoi(), atol()

str2int(src, radix, lower, upper, &val)

converts the string pointed to by src to an integer and stores it in

val. It skips leading spaces and tabs (but not newlines, formfeeds,

backspaces), then it accepts an optional sign and a sequence of digits

in the specified radix. The result should satisfy lower <= *val <= upper.

The result is a pointer to the first character after the number;

trailing spaces will NOT be skipped.

If an error is detected, the result will be NullS, the value put

in val will be 0, and errno will be set to

EDOM if there are no digits

ERANGE if the result would overflow or otherwise fail to lie

within the specified bounds.

Check that the bounds are right for your machine.

This looks amazingly complicated for what you probably thought was an

easy task. Coping with integer overflow and the asymmetric range of

twos complement machines is anything but easy.

So that users of atoi and atol can check whether an error occured,

I have taken a wholly unprecedented step: errno is CLEARED if this

call has no problems.

*/

#include "strings.h"

#include "ctypes.h"

#include

extern int errno;

/* CHECK THESE CONSTANTS FOR YOUR MACHINE!!! */

#if pdp11

# define MaxInt 0x7fffL /* int = 16 bits */

# define MinInt 0x8000L

# define MaxLong 0x7fffffffL /* long = 32 bits */

# define MinLong 0x80000000L

#else !pdp11

# define MaxInt 0x7fffffffL /* int = 32 bits */

# define MinInt 0x80000000L

# define MaxLong 0x7fffffffL /* long = 32 bits */

# define MinLong 0x80000000L

#endif pdp11

char *str2int(src, radix, lower, upper, val)

register char *src;

register int radix;

long lower, upper, *val;

{

int sign; /* is number negative (+1) or positive (-1) */

int n; /* number of digits yet to be converted */

long limit; /* "largest" possible valid input */

long scale; /* the amount to multiply next digit by */

long sofar; /* the running value */

register int d; /* (negative of) next digit */

char *answer;

/* Make sure *val is sensible in case of error */

*val = 0;

/* Check that the radix is in the range 2..36 */

if (radix < 2 || radix > 36) {

errno = EDOM;

return NullS;

}

/* The basic problem is: how do we handle the conversion of

a number without resorting to machine-specific code to

check for overflow? Obviously, we have to ensure that

no calculation can overflow. We are guaranteed that the

"lower" and "upper" arguments are valid machine integers.

On sign-and-magnitude, twos-complement, and ones-complement

machines all, if +|n| is representable, so is -|n|, but on

twos complement machines the converse is not true. So the

"maximum" representable number has a negative representative.

Limit is set to min(-|lower|,-|upper|); this is the "largest"

number we are concerned with. */

/* Calculate Limit using Scale as a scratch variable */

if ((limit = lower) > 0) limit = -limit;

if ((scale = upper) > 0) scale = -scale;

if (scale < limit) limit = scale;

/* Skip leading spaces and check for a sign.

Note: because on a 2s complement machine MinLong is a valid

integer but |MinLong| is not, we have to keep the current

converted value (and the scale!) as *negative* numbers,

so the sign is the opposite of what you might expect.

Should the test in the loop be isspace(*src)?

*/

while (*src == ' ' || *src == '\t') src++;

sign = -1;

if (*src == '+') src++; else

if (*src == '-') src++, sign = 1;

/* Check that there is at least one digit */

if (_c2type[1+ *src] >= radix) {

errno = EDOM;

return NullS;

}

/* Skip leading zeros so that we never compute a power of radix

in scale that we won't have a need for. Otherwise sticking

enough 0s in front of a number could cause the multiplication

to overflow when it neededn't.

*/

while (*src == '0') src++;

/* Move over the remaining digits. We have to convert from left

to left in order to avoid overflow. Answer is after last digit.

*/

for (n = 0; _c2type[1+ *src++] < radix; n++) ;

answer = --src;

/* The invariant we want to maintain is that src is just

to the right of n digits, we've converted k digits to

sofar, scale = -radix**k, and scale < sofar < 0. Now

if the final number is to be within the original

Limit, we must have (to the left)*scale+sofar >= Limit,

or (to the left)*scale >= Limit-sofar, i.e. the digits

to the left of src must form an integer <= (Limit-sofar)/(scale).

In particular, this is true of the next digit. In our

incremental calculation of Limit,

IT IS VITAL that (-|N|)/(-|D|) = |N|/|D|

*/

for (sofar = 0, scale = -1; --n >= 0; ) {

d = _c2type[1+ *--src];

if (-d < limit) {

errno = ERANGE;

return NullS;

}

limit = (limit+d)/radix, sofar += d*scale;

if (n != 0) scale *= radix; /* watch out for overflow!!! */

}

/* Now it might still happen that sofar = -32768 or its equivalent,

so we can't just multiply by the sign and check that the result

is in the range lower..upper. All of this caution is a right

pain in the neck. If only there were a standard routine which

says generate thus and such a signal on integer overflow...

But not enough machines can do it *SIGH*.

*/

if (sign < 0 && sofar < -MaxLong /* twos-complement problem */

|| (sofar*=sign) < lower || sofar > upper) {

errno = ERANGE;

return NullS;

}

*val = sofar;

errno = 0; /* indicate that all went well */

return answer;

}

int atoi(src)

char *src;

{

long val;

str2int(src, 10, MinInt, MaxInt, &val);

return (int)val;

}

long atol(src)

char *src;

{

long val;

str2int(src, 10, MinLong, MaxLong, &val);

return val;

}

Very nice! Thank you for this wonderful archive. I wonder why I found it only now. Long live the BBS file archives!

This is so awesome! 😀 I’d be cool if you could download an entire archive of this at once, though.

But one thing that puzzles me is the “mtswslnkmcjklsdlsbdmMICROSOFT” string. There is an article about it here. It is definitely worth a read: http://www.os2museum.com/wp/mtswslnk/