atoi() & itoa()&atol()&ltoa()函数的实现

#include "stdio.h"
#include "conio.h"
#include <ctype.h>
#include <stdlib.h>
 
typedef long long  __int64;   //64位 需要设备支持64 否则结果是不对的
/**************************************/
 
long  atol(const char *nptr)
{
    int c; /* current char */
    long total; /* current total */
    int sign; /* if ''-'', then negative, otherwise positive */
 
/* skip whitespace */
    while ( isspace((int)(unsigned char)*nptr) )
        ++nptr;
 
    c = (int)(unsigned char)*nptr++;
    sign = c; /* save sign indication */
    if (c == '-' || c == '+')
        c = (int)(unsigned char)*nptr++; /* skip sign */
 
    total = 0;
 
    while (isdigit(c)) {
        total = 10 * total + (c - '0'); /* accumulate digit */
        c = (int)(unsigned char)*nptr++; /* get next char */
    }
 
    if (sign == '-')
        return -total;
    else
        return total; /* return result, negated if necessary */
}
 
 
 
int atoi(const char *nptr)
{
    return (int)atol(nptr);
}
 
#ifndef _NO_INT64
 
__int64  _atoi64(const char *nptr)
{
    int c; /* current char */
    __int64 total; /* current total */
    int sign; /* if ''-'', then negative, otherwise positive */
 
    /* skip whitespace */
    while ( isspace((int)(unsigned char)*nptr) )
        ++nptr;
 
    c = (int)(unsigned char)*nptr++;
    sign = c; /* save sign indication */
    if (c == '-' || c == '+')
    c = (int)(unsigned char)*nptr++; /* skip sign */
    
    total = 0;
 
    while (isdigit(c)) {
        total = 10 * total + (c - '0'); /* accumulate digit */
    c = (int)(unsigned char)*nptr++; /* get next char */
}
 
    if (sign == '-')
        return -total;
    else
        return total; /* return result, negated if necessary */
}
 
#endif /* _NO_INT64 */
 
 
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)
    {
 
        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;
} 

char* _ltoa(long value, char* string, int radix)
{
    char tmp[33];
    char* tp = tmp;
    long i;
    long v;
    int sign;
    char* sp;

    if (radix > 36 || radix <= 1)
    {

        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;
}