itoa、ltoa

#include <stdlib.h>
    
/*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)
    {
        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)
    {
        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)
    {
        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;
}

来源：https://www.cnblogs.com/s3320/p/11959314.html