Base64 解码【代码实现】

前往Base64 编码【代码实现】

C++

#include <algorithm>
#include <iostream>
#include <string>
#include <vector>typedef unsigned char ubyte;
const auto BASE64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";std::vector<ubyte> encode(const std::vector<ubyte>& source) {
    auto it = source.cbegin();auto end = source.cend();std::vector<ubyte> sink;while (it != end) {
    auto b1 = *it++;int acc;sink.push_back(BASE64[b1 >> 2]);            // first output (first six bits from b1)acc = (b1 & 0x3) << 4;                      // last two bits from b1if (it != end) {
    auto b2 = *it++;acc |= (b2 >> 4);                       // first four bits from b2sink.push_back(BASE64[acc]);            // second outputacc = (b2 & 0xF) << 2;                  // last four bits from b2if (it != end) {
    auto b3 = *it++;acc |= (b3 >> 6);                   // first two bits from b3sink.push_back(BASE64[acc]);        // third outputsink.push_back(BASE64[b3 & 0x3F]);  // fouth output (final six bits from b3)} else {
    sink.push_back(BASE64[acc]);        // third outputsink.push_back('=');                // fourth output (1 byte padding)}} else {
    sink.push_back(BASE64[acc]);            // second outputsink.push_back('=');                    // third output (first padding byte)sink.push_back('=');                    // fourth output (second padding byte)}}return sink;
}int findIndex(ubyte val) {
    if ('A' <= val && val <= 'Z') {
    return val - 'A';}if ('a' <= val && val <= 'z') {
    return val - 'a' + 26;}if ('0' <= val && val <= '9') {
    return val - '0' + 52;}if ('+' == val) {
    return 62;}if ('/' == val) {
    return 63;}return -1;
}std::vector<ubyte> decode(const std::vector<ubyte>& source) {
    if (source.size() % 4 != 0) {
    throw new std::runtime_error("Error in size to the decode method");}auto it = source.cbegin();auto end = source.cend();std::vector<ubyte> sink;while (it != end) {
    auto b1 = *it++;auto b2 = *it++;auto b3 = *it++; // might be first padding byteauto b4 = *it++; // might be first or second padding byteauto i1 = findIndex(b1);auto i2 = findIndex(b2);int acc;acc = i1 << 2;          // six bits came from the first byteacc |= i2 >> 4;         // two bits came from the first bytesink.push_back(acc);    // output the first byteif (b3 != '=') {
    auto i3 = findIndex(b3);acc = (i2 & 0xF) << 4;  // four bits came from the second byteacc |= i3 >> 2;         // four bits came from the second bytesink.push_back(acc);    // output the second byteif (b4 != '=') {
    auto i4 = findIndex(b4);acc = (i3 & 0x3) << 6;  // two bits came from the third byteacc |= i4;              // six bits came from the third bytesink.push_back(acc);    // output the third byte}}}return sink;
}int main() {
    using namespace std;string data = "VG8gZXJyIGlzIGh1bWFuLCBidXQgdG8gcmVhbGx5IGZvdWwgdGhpbmdzIHVwIHlvdSBuZWVkIGEgY29tcHV0ZXIuCiAgICAtLVBhdWwgUi5FaHJsaWNo";vector<ubyte> datav{
     begin(data), end(data) };cout << data << "\n\n";auto decoded = decode(datav);std::for_each(cbegin(decoded), cend(decoded), [](char c) {
     cout << c; });cout << '\n';return 0;
}

输出：

VG8gZXJyIGlzIGh1bWFuLCBidXQgdG8gcmVhbGx5IGZvdWwgdGhpbmdzIHVwIHlvdSBuZWVkIGEgY29tcHV0ZXIuCiAgICAtLVBhdWwgUi5FaHJsaWNo

To err is human, but to really foul things up you need a computer.
–Paul R.Ehrlich

Go

package mainimport ("encoding/base64""fmt"
)func main() {
    msg := "Rosetta Code Base64 decode data task"fmt.Println("Original :", msg)encoded := base64.StdEncoding.EncodeToString([]byte(msg))fmt.Println("\nEncoded :", encoded)decoded, err := base64.StdEncoding.DecodeString(encoded)if err != nil {
    fmt.Println(err)return}fmt.Println("\nDecoded :", string(decoded))
}

输出：

Original : Rosetta Code Base64 decode data task
Encoded : Um9zZXR0YSBDb2RlIEJhc2U2NCBkZWNvZGUgZGF0YSB0YXNr
Decoded : Rosetta Code Base64 decode data task

Kotlin

import java.util.Base64fun main() {
    val data ="VG8gZXJyIGlzIGh1bWFuLCBidXQgdG8gcmVhbGx5IGZvdWwgdGhpbmdzIHVwIHlvdSBuZWVkIGEgY29tcHV0ZXIuCiAgICAtLSBQYXVsIFIuIEVocmxpY2g="val decoder = Base64.getDecoder()val decoded = decoder.decode(data)val decodedStr = String(decoded, Charsets.UTF_8)println(decodedStr)
}

输出：

To err is human, but to really foul things up you need a computer.
– Paul R. Ehrlich

Ruby

require 'base64'perl6_example ='
VG8gZXJyIGlzIGh1bWFuLCBidXQgdG8gcmVhbGx5IGZvdWwgdGhpbmdzIHVwIHlvdSBuZWVkIGEgY2
9tcHV0ZXIuCiAgICAtLSBQYXVsIFIuIEVocmxpY2g=
'
puts Base64.decode64 perl6_example

输出：

To err is human, but to really foul things up you need a computer.
– Paul R. Ehrlich