itoa atoi ltoa ultoa函数原型实现

/*
* FILE: lib/crtdll/stdlib/itoa.c
* PURPOSE: converts a integer to ascii
* PROGRAMER:
* UPDATE HISTORY:
* 1995: Created
* 1998: Added ltoa Boudewijn Dekker
*/

itoa函数原型
#include
#include
#include
/*整形转字符型*/
char *itoa(int value, char *string, int radix)
{
char tmp[33];
char *tp = tmp;
int i;
unsigned v;
int sign;
char *sp;

if (radix > 36 || radix <= 1)
{
__set_errno(EDOM);
return 0;
}

sign = (radix == 10 && value < 0);
if (sign)
v = -value;
else
v = (unsigned)value;
while (v || tp == tmp)
{
i = v % radix;
v = v / radix;
if (i < 10)
*tp++ = i+'0';
else
*tp++ = i + 'a' - 10;
}

if (string == 0)
string = (char *)malloc((tp-tmp)+sign+1);
sp = string;

if (sign)
*sp++ = '-';
while (tp > tmp)
*sp++ = *--tp;
*sp = 0;
return string;
}

/*长整形转字符型*/
char *ltoa(long value, char *string, int radix)
{
char tmp[33];
char *tp = tmp;
long i;
unsigned long v;
int sign;
char *sp;

if (radix > 36 || radix <= 1)
{
__set_errno(EDOM);
return 0;
}

sign = (radix == 10 && value < 0);
if (sign)
v = -value;
else
v = (unsigned long)value;
while (v || tp == tmp)
{
i = v % radix;
v = v / radix;
if (i < 10)
*tp++ = i+'0';
else
*tp++ = i + 'a' - 10;
}

if (string == 0)
string = (char *)malloc((tp-tmp)+sign+1);
sp = string;

if (sign)
*sp++ = '-';
while (tp > tmp)
*sp++ = *--tp;
*sp = 0;
return string;
}
/*无符号长整形转字符型*/
char *_ultoa(unsigned long value, char *string, int radix)
{
char tmp[33];
char *tp = tmp;
long i;
unsigned long v = value;
char *sp;

if (radix > 36 || radix <= 1)
{
__set_errno(EDOM);
return 0;
}


while (v || tp == tmp)
{
i = v % radix;
v = v / radix;
if (i < 10)
*tp++ = i+'0';
else
*tp++ = i + 'a' - 10;
}
if (string == 0)
string = (char *)malloc((tp-tmp)+1);
sp = string;

while (tp > tmp)
*sp++ = *--tp;
*sp = 0;
return string;
}

/*字符串转整形*/

#include "iostream.h"
int toi(const char * s)
{
int n = 0;

while(!(*s >= '0' && *s <= '9'))
s++;

while(*s >= '0' && *s <= '9')
{
n *= 10;
n += *s - '0';
s++;
}
return n;
}