#include <string>
#include <vector>
<p>static const std::string base64_chars =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";</p><p>std::string base64_encode(const std::string& input) {
std::string output;
output.reserve(((input.length() + 2) / 3) * 4); // 预分配空间</p><pre class='brush:php;toolbar:false;'>size_t i = 0;
while (i < input.length()) {
    unsigned char b0 = input[i++];
    unsigned char b1 = (i < input.length()) ? input[i++] : 0;
    unsigned char b2 = (i < input.length()) ? input[i++] : 0;

    unsigned char p0 = b0 >> 2;
    unsigned char p1 = ((b0 & 0x03) << 4) | (b1 >> 4);
    unsigned char p2 = ((b1 & 0x0f) << 2) | (b2 >> 6);
    unsigned char p3 = b2 & 0x3f;

    output.push_back(base64_chars[p0]);
    output.push_back(base64_chars[p1]);
    output.push_back((i > input.length() - 2) ? '=' : base64_chars[p2]);
    output.push_back((i > input.length() - 1) ? '=' : base64_chars[p3]);
}
return output;

}

#include <stdexcept>
#include <cctype>
<p>std::string base64_decode(const std::string& input) {
// 忽略空白符（如换行、空格），但不自动跳过非法字符
std::string clean;
for (char c : input)
if (!std::isspace(static_cast<unsigned char>(c))) clean += c;</p><pre class='brush:php;toolbar:false;'>if (clean.empty()) return {};

size_t len = clean.length();
if (len % 4 != 0) throw std::invalid_argument("Base64 string length not multiple of 4");

// 检查结尾填充是否合法：最多两个 '='，且必须在末尾
size_t pad = 0;
if (len >= 2 && clean[len-1] == '=') pad++;
if (len >= 2 && clean[len-2] == '=') pad++;

std::string output;
output.reserve((len * 3) / 4 - pad);

std::vector<int> lookup(256, -1);
for (size_t i = 0; i < base64_chars.length(); ++i)
    lookup[static_cast<unsigned char>(base64_chars[i])] = static_cast<int>(i);

for (size_t i = 0; i < len; i += 4) {
    int p0 = lookup[static_cast<unsigned char>(clean[i])];
    int p1 = lookup[static_cast<unsigned char>(clean[i+1])];
    int p2 = (i + 2 < len && clean[i+2] != '=') ? lookup[static_cast<unsigned char>(clean[i+2])] : 0;
    int p3 = (i + 3 < len && clean[i+3] != '=') ? lookup[static_cast<unsigned char>(clean[i+3])] : 0;

    if (p0 == -1 || p1 == -1 || (i+2 < len && clean[i+2] != '=' && p2 == -1) ||
        (i+3 < len && clean[i+3] != '=' && p3 == -1))
        throw std::invalid_argument("Invalid Base64 character");

    unsigned char b0 = (p0 << 2) | (p1 >> 4);
    unsigned char b1 = ((p1 & 0x0f) << 4) | (p2 >> 2);
    unsigned char b2 = ((p2 & 0x03) << 6) | p3;

    output.push_back(b0);
    if (i + 2 < len && clean[i+2] != '=') output.push_back(b1);
    if (i + 3 < len && clean[i+3] != '=') output.push_back(b2);
}
return output;

}

#include <iostream>
#include <cassert>
<p>int main() {
// 示例1：普通字符串
std::string s1 = "Hello, 世界";
std::string enc1 = base64_encode(s1);
std::string dec1 = base64_decode(enc1);
assert(dec1 == s1);
std::cout << "Text: " << enc1 << "\n"; // SGVsbG8sIOS4lueVjA==</p><pre class='brush:php;toolbar:false;'>// 示例2：含空字节的二进制数据
std::string bin = "ABC\0XYZ";
std::string enc2 = base64_encode(bin);
std::string dec2 = base64_decode(enc2);
assert(dec2 == bin);
std::cout << "Binary len: " << enc2 << " (" << dec2.length() << " bytes)\n";

return 0;

}