将长整数(十进制)转换为基数 36 字符串(C 中的 strtol 反转函数) [英] Convert long integer(decimal) to base 36 string (strtol inverted function in C)

问题描述

我可以使用 strtol 函数将基于 base36 的值(保存为字符串)转换为 long int:

I can use the strtol function for turning a base36 based value (saved as a string) into a long int:

long int val = strtol("ABCZX123", 0, 36);

是否有一个标准函数可以反转这个?也就是把long int val变量转成base36字符串，再得到"ABCZX123"?

Is there a standard function that allows the inversion of this? That is, to convert a long int val variable into a base36 string, to obtain "ABCZX123" again?

推荐答案

这个没有标准函数.你需要自己写一个.

There's no standard function for this. You'll need to write your own one.

使用示例:https://godbolt.org/z/MhRcNA

const char digits[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

char *reverse(char *str)
{
    char *end = str;
    char *start = str;

    if(!str || !*str) return str;
    while(*(end + 1)) end++;
    while(end > start)
    {
        int ch = *end;
        *end-- = *start;
        *start++ = ch;
    }
    return str;
}

char *tostring(char *buff, long long num, int base)
{
    int sign = num < 0;
    char *savedbuff = buff;

    if(base < 2 || base >= sizeof(digits)) return NULL;
    if(buff)
    {
        do
        {   
            *buff++ = digits[abs(num % base)];
            num /= base;
        }while(num);
        if(sign)
        {
            *buff++ = '-';
        }
        *buff = 0;
        reverse(savedbuff);
    }
    return savedbuff;
}

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