這幾天在較為認真的研究基于哈夫曼編碼的文件壓縮及解壓，費了點時間，在這分享一下：

這里用鏈式結構，非順序表結構；

文件壓縮：

1.獲取文件信息（這里采用TXT格式文本）；

2.壓縮文件；

3.寫配置文件（便于解壓時用，無非就是存放原文件的索引之類的，比如說，文件中某個字符出現的個數，記錄下來）

4.解壓縮，使用壓縮后的文件和配置文件解壓文件；

5.用比對軟件，比對解壓后的文件和源文件是否相同；

下面慢慢解析：

先看一個文件信息類：

typedef long long LongType; struct FileInfo {unsigned char _ch; //字符LongType _count; //字符出現次數string _code; //字符對應的哈夫曼編碼 FileInfo(unsigned char ch = 0):_ch(ch),_count(0){}FileInfo operator+(const FileInfo& x){FileInfo tmp;tmp._count = this->_count + x._count;return tmp;}bool operator !=(const FileInfo& x) const{return this->_count != x._count;} };bool operator<(const FileInfo info1,const FileInfo info2) {return info1._count < info2._count; }此為一個文件信息的類結構，包含字符，字符對應出現的次數，以及這個字符對應的哈夫曼編碼（能看到這篇博客的星弟，對哈夫曼編碼不會陌生，這里不再強調）

除了統計字符出現的次數及哈夫曼編碼，還完成了幾個運算符的重載

要獲取哈夫曼編碼，就得建立哈夫曼樹，建立哈夫曼樹用最小堆取操作，以下是最小堆建立過程

// 小堆 template<class T> struct Less {bool operator() (const T& l, const T& r){return l < r; // operator<}};template<class T> struct Greater {bool operator() (const T& l, const T& r){return l > r; // operator<} };template<class T, class Compare = Less<T>> class Heap { public:Heap(){}Heap(const T* a, size_t size){for (size_t i = 0; i < size; ++i){_arrays.push_back(a[i]);}// 建堆for(int i = (_arrays.size()-2)/2; i >= 0; --i){AdjustDown(i);}}void Push(const T& x){_arrays.push_back(x);AdjustUp(_arrays.size()-1);}void Pop(){assert(_arrays.size() > 0);swap(_arrays[0], _arrays[_arrays.size() - 1]);_arrays.pop_back();AdjustDown(0);}T& Top(){assert(_arrays.size() > 0);return _arrays[0];}bool Empty(){return _arrays.empty();}int Size(){return _arrays.size();}void AdjustDown(int root){int child = root*2 + 1;// Compare com;while (child < _arrays.size()){// 比較出左右孩子中小的那個if (child+1<_arrays.size() &&*_arrays[child+1] < _arrays[child])//if(child+1<_arrays.size() &&// com(_arrays[child+1],_arrays[child])){++child;}if(*_arrays[child] < _arrays[root])//if(com(_arrays[child],_arrays[root])){swap(_arrays[child], _arrays[root]);root = child;child = 2*root+1;}else{break;}}}void AdjustUp(int child){int parent = (child-1)/2;//while (parent >= 0)while (child > 0){if (*_arrays[child] < _arrays[parent]){swap(_arrays[parent], _arrays[child]);child = parent;parent = (child-1)/2;}else{break;}}}public:vector<T> _arrays; };最小堆里也完成了很多接口，包括push ?pop等

然后就是幾個壓縮和解壓的函數接口

1.根據哈夫曼樹獲取哈夫曼變慢：

void _GenerateHuffmanCode(HuffmanTreeNode<FileInfo>* root){if (root == nullptr){return;}_GenerateHuffmanCode(root->_left);_GenerateHuffmanCode(root->_right);//當前節點為葉子節點為空 才生成哈夫曼編碼if (root->_left == nullptr && root->_right == nullptr){HuffmanTreeNode<FileInfo>* cur = root;HuffmanTreeNode<FileInfo>* parent = cur->_parent;string& code = _infos[cur->_weight._ch]._code;while (parent){if (parent->_left == cur){code += '1';}else if (parent->_right == cur){code += '0';}cur = parent;parent = cur->_parent;}reverse(code.begin(), code.end());}}

2.根據最小堆建立哈夫曼樹；

void CreateTree(T *a, size_t size, const T& invalid){assert(a);Heap<HuffmanTreeNode<T>*> s1; //草 終于發現問題 在這里 （堆里放的是指針，類型一定要對）//找兩個最小的元素for (size_t i = 0; i < size; ++i){if (a[i] != invalid){HuffmanTreeNode<T>* node = new HuffmanTreeNode<T>(a[i]);s1.Push(node);}}while (s1.Size() > 1){HuffmanTreeNode<T>* left = s1.Top();s1.Pop();HuffmanTreeNode<T>* right = s1.Top();s1.Pop();HuffmanTreeNode<T>* parent = new HuffmanTreeNode<T>(left->_weight + right->_weight);parent->_left = left;parent->_right = right;left->_parent = parent;right->_parent = parent;s1.Push(parent);}_root = s1.Top();s1.Pop();}

3.讀取文本文件中的一行：

bool _ReadLine(FILE *fOutLogFile, string& line){char ch = fgetc(fOutLogFile);if (feof(fOutLogFile))return false;else{if (ch == '\n'){line += ch;ch = fgetc(fOutLogFile);}while (ch != '\n'){line += ch;ch = fgetc(fOutLogFile);}return true;}}
4.文件壓縮

//文件壓縮bool Compress(const char* filename){//1.打開一個文件，統計文件字符出現的次數//2.生成對應的哈弗曼編碼//3.壓縮文件//4.寫配置文件，方便解壓縮assert(filename);FILE *fOut = fopen(filename, "rb");assert(fOut);//統計文件字符出現的次數unsigned char ch = fgetc(fOut);while (!feof(fOut)) //文件結束{_infos[ch]._count++;ch = fgetc(fOut);}HuffmanTree<FileInfo> ht;FileInfo invalid;ht.CreateTree(_infos, 256, invalid);//哈夫曼編碼_GenerateHuffmanCode(ht.GetRoot());string compressFile = filename;compressFile += ".huf";//壓縮后的文件名 后綴為《輸入文件名+.huf》FILE *finCompress = fopen(compressFile.c_str(), "wb"); //獲取string中的C字符串assert(finCompress);fseek(fOut, 0, SEEK_SET);//將文件指針移到開頭char cha = fgetc(fOut);unsigned char inch = 0;int index = 0; //一個字節的八位while (!feof(fOut)){string& code = _infos[(unsigned char)cha]._code;for (size_t i = 0; i < code.size(); ++i){inch <<= 1; //低位向高位進if (code[i] == '1'){inch |= 1;}if (++index == 8){fputc(inch, finCompress); //夠8位，裝進文件index = 0; //重新一輪開始inch = 0;}}cha = fgetc(fOut);}fclose(fOut);//如果index = 0 說明 上邊8位剛好存滿 不等 下一個自己又出來了if (index != 0) //處理最后一個字符不夠的問題{inch <<= (8 - index); //最高位必須裝上 后邊的浪費掉fputc(inch, finCompress);}fclose(finCompress);}
5.寫配置文件：

string logFile = filename;logFile += ".log";FILE *Log = fopen(logFile.c_str(), "wb");assert(Log);string chInfo;char str[128] = {0}; //沒空間 不可以for (size_t i = 1; i < 256; ++i){if (_infos[i]._count > 0){chInfo += _infos[i]._ch;chInfo += ',';chInfo += _itoa(_infos[i]._count,str,10);chInfo += '\n';fputs(chInfo.c_str(), Log);chInfo.clear();}}fclose(Log);
6.最后的文件解壓：

//重構文件void _RestoreFiles(HuffmanTreeNode<FileInfo> *root, const char* Fileneme,long long size){assert(root);//原壓縮文件string name = Fileneme;name += ".huf";FILE* Out = fopen(name.c_str(),"rb");assert(Out);string restorefilename = Fileneme;restorefilename += ".over";FILE *over = fopen(restorefilename.c_str(),"wb");assert(over);int pos = 8;long long poss = size;unsigned char chz = fgetc(Out);while (poss>0){HuffmanTreeNode<FileInfo>* cur = nullptr;cur = root;while (cur->_left != nullptr || cur->_right != nullptr){pos--;unsigned char temp = chz >> pos;int ch = 1 & temp;if (ch == 0){cur = cur->_right;}else if (ch == 1){cur = cur->_left;}if (pos == 0){chz = fgetc(Out);pos = 8;}}fputc(cur->_weight._ch, over);poss--;}fclose(Out);fclose(over);}void UnCompress(const char* Fileneme)//解壓縮{//1.打開日志文件//2.根據信息還原哈夫曼樹//3.還原信息；string UnCompressneme = Fileneme;UnCompressneme += ".log";FILE *fOutLogFile = fopen(UnCompressneme.c_str(), "rb");assert(fOutLogFile);string line;while (_ReadLine(fOutLogFile, line)){unsigned char ch = line[0];_infos[ch]._count = atoi(line.substr(2).c_str());line.clear();} HuffmanTree<FileInfo> f;FileInfo invalid;f.CreateTree(_infos, 256, invalid);//根據重建的哈夫曼樹 還原文件；long long size = f.GetRoot()->_weight._count;_RestoreFiles(f.GetRoot(), Fileneme,size);}到此，此項目基本完成；如遇問題，希望留言，隨時解答，如有見解，跪求賜教！

轉載于:https://www.cnblogs.com/li-ning/p/9490022.html

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