c++模拟foreach关键字

最近研究《the art of c++》一书，其中，第四章扩展了一些C++的关键词，比如foreach，cases，typeof等等。

下面是第四章foreach功能的复现。

功能：翻译文件中的foreach（[type] v in array），为

for( [type] v = array[0], _ia = 0;

       _ia < sizeof(array)/sizeof(array[0]);

       _ia++, v = array[_ia])

Debug时，需要创建foreach.exp2文件，文件内写需要翻译的代码。

#include <iostream>#include <string>#include <fstream>using namespace std;ifstream ifile;ofstream ofile;bool getToken(string &token);void foreach();void skipSpaces();string indent;class SyntaxError{string errorString;public:SyntaxError(string err){errorString = err;}string getError(){return errorString;}};int main(int argc, char** argv){#ifndef DEBUGif(argc != 3){cout<<"usage:trans <inputfile> <outputfile>/n";return -1;}#endif#ifdef DEBUGargv[1] = "foreach.exp2";argv[2] = "foreach.cpp";#endififile.open(argv[1]);if(!ifile){cout<<"input file not exist!/n";return 1;}ofile.open(argv[2]);if(!ofile){cout<<"output file cannot open!/n";return 2;}ofile<<"//This file translate from file ["<<argv[1]<<"]"<<endl;try{string token;while(getToken(token)){//line start with //if(token == "//"){do{ofile<<token;}while(getToken(token) && token.find('/n') == string::npos);ofile << token;}//line start with /*else if(token == "/*"){do{ofile<<token;}while(getToken(token) && token != "*/");ofile << token;}//token "else if(token == "/""){do{ofile<<token;}while(getToken(token) && token != "/"");ofile << token;}else if(token == "foreach"){foreach();}elseofile<<token;}}catch(SyntaxError exc){cout << exc.getError()<<endl;return -1;}return 0;}static bool isIndent = true;bool getToken(string &token){char ch;//char ch2;token = "";//white spacech = ifile.get();if(!ifile)return false;if(isspace(ch)){do{token += ch;if(ch == '/n'){indent = "";isIndent = true;}else if(isIndent)indent += ch;}while(isspace(ch = ifile.get()));ifile.putback(ch);return true;}isIndent = false;//charactorif(isalpha(ch) || ch == '_'){do{token += ch;ch = ifile.get();}while(isalpha(ch)|| isdigit(ch)|| ch == '_');ifile.putback(ch);return true;}//numberif(isdigit(ch)){do{token += ch;ch = ifile.get();}while(isdigit(ch)|| ch == '.'|| ch == 'e'|| ch == 'E'|| ch == '+'|| ch == '-');ifile.putback(ch);return true;}///"if(ch == '//'){char ch2;ch2 = ifile.get();if(ch2 == '"'){token += ch;token += ch2;ch = ifile.get();}else{ifile.putback(ch2);}}//'"if(ch == '/''){char ch2;ch2 = ifile.get();if(ch2 == '"'){token += ch;token += ch2;return true;}else{ifile.putback(ch2);}}// // or /*if(ch == '/'){char ch2;ch2 = ifile.get();if(ch2 == '/' || ch2 == '*'){token += ch;token += ch2;}else{ifile.putback(ch2);}return true;}// */if(ch == '*'){char ch2 = ifile.get();if(ch2 == '/'){token += ch;token += ch2;}else{token += ch;ifile.putback(ch2);}return true;}token += ch;return true;}void skipSpaces(){char ch;ch = ifile.get();while(isspace(ch)){ch = ifile.get();}ifile.putback(ch);}void foreach(){string token;string varName;string arrayName;ofile<<"for";getToken(token);//foreach(Tif(token[0] != '(')throw SyntaxError(string("foreach syntax error 1"));ofile<<token;getToken(token);ofile<<token<<" ";skipSpaces();getToken(token);//varvarName = token;skipSpaces();getToken(token);//inif(token != "in")throw SyntaxError(string("foreach syntax error 2"));skipSpaces();getToken(token);//arrayarrayName = token;ofile<<varName<<" = "<<arrayName<<"[0], _ia = 0;/n";ofile<<indent<<"_ia < sizeof("<<arrayName<<")/sizeof("<<arrayName<<"[0]);/n";ofile<<indent<<"_ia++,"<<varName<<"="<<arrayName<<"[_ia]";skipSpaces();getToken(token);if(token != ")")throw SyntaxError(string("foreach syntax error 3"));ofile << token;}