c++特别大的整数进制转换函数

C++中可以使用标准库中的`stringstream`来实现大整数进制转换，具体实现方法如下：

#include <iostream>
#include <sstream>
#include <string>
#include <algorithm>

using namespace std;

// 将十进制数转换为其他进制
string dec_to_any(int num, int base) {
    stringstream ss;
    string result = "";
    bool negative = false;

    if (num < 0) {
        negative = true;
        num = -num;
    }

    while (num) {
        int remainder = num % base;
        if (remainder < 10) {
            ss << remainder;
        } else {
            ss << (char)('A' + remainder - 10);
        }
        num /= base;
    }

    ss >> result;
    if (negative) {
        result += "-";
    }

    reverse(result.begin(), result.end());
    return result;
}

// 将其他进制数转换为十进制
int any_to_dec(string num, int base) {
    int result = 0;
    bool negative = false;

    if (num[0] == '-') {
        negative = true;
        num.erase(num.begin());
    }

    for (int i = 0; i < num.size(); i++) {
        int digit = 0;
        if (num[i] >= '0' && num[i] <= '9') {
            digit = num[i] - '0';
        } else {
            digit = num[i] - 'A' + 10;
        }
        result = result * base + digit;
    }

    if (negative) {
        result = -result;
    }

    return result;
}

int main() {
    int num = 1234567890;
    int base1 = 2, base2 = 16;
    string result1 = dec_to_any(num, base1);
    int result2 = any_to_dec(result1, base1);
    string result3 = dec_to_any(num, base2);
    int result4 = any_to_dec(result3, base2);

    cout << "num: " << num << endl;
    cout << "base " << base1 << ": " << result1 << endl;
    cout << "back to decimal: " << result2 << endl;
    cout << "base " << base2 << ": " << result3 << endl;
    cout << "back to decimal: " << result4 << endl;

    return 0;
}

在上述代码中，`dec_to_any`函数将一个十进制数转换为其他进制的数，`any_to_dec`函数将其他进制的数转换为十进制数，其中`base`参数表示需要转换的进制。

代码中使用了`stringstream`来将数字转换为字符串，`reverse`函数用于翻转字符串。