C++ ifstream::putback方法代码示例

void lex(ifstream& ifs) {
    // Reserve
    reserve();

    // Vector of tokens in one statement (statement ends with semicolon)
    vector<Token> oneStmtToken;
    char current;
    while ( (current = ifs.get()) != EOF ) {
        int type = getType(current);
        if ( type == SPACE ) {
            // Ignore
        } else if ( type == DIGIT ) {
            // Get the actual number
            int v = 0;
            int startCol = _col;
            do {
                v = 10 * v + current - '0';
                current = ifs.get();
            } while ( getType(current) == DIGIT );
            ifs.putback(current);
            revert(current);

            Token num(NUM, _line, startCol, v);
            oneStmtToken.push_back(num);
        } else if ( type == LETTER ) {
            // Get the id
            string buffer;
            int subType;
            int startCol = _col;
            do {
                buffer += current;
                current = ifs.get();
                subType = getType(current);
            } while ( subType == LETTER || subType == DIGIT );
            ifs.putback(current);
            revert(current);

            // If it is keyword
            int tag = symbol.find(buffer)->second.tag;
            if ( tag >= 256 && tag <= 269 ) {
                Token keyword(tag, _line, startCol, -1, buffer);
                oneStmtToken.push_back(keyword);
            } else { // It is identifier 
                Token keyword(ID, _line, startCol, -1, buffer);
                oneStmtToken.push_back(keyword);
            }
        } else if ( type == DELIMIT ) {
            // Convert char to string to be stored in Token
            stringstream ss;
            ss << current;
            string cur;
            ss >> cur;

            Token delimit(current, _line, _col, -1, cur);
            oneStmtToken.push_back(delimit);
        } else if ( type == REGEXSTART ) {

void PNMFileUtils::extractToken(ifstream &inputStream,
                                char *token,
                                int maxSize)
{
  int count = 0;
  char ch;
  
  // skip whitespace and comments
  do
  {
    inputStream.read((char *)&ch, sizeof(char));
    // if a comment char is found then read till the next "\n"
    if(ch == '#')
      while(ch != '\n')
        inputStream.read((char *)&ch, sizeof(char *));
  }
  while(ch == ' ' || ch == '\t' || ch == '\n');
  
  // copy data into token
  do
  {
    if(count >= maxSize - 1)
      throw runtime_error("Token too large");
    token[count++] = ch;
    inputStream.read((char *)&ch, sizeof(char));
  }
  while(ch != ' ' && ch != '\t' && ch != '\n' && ch != '.');
  
  inputStream.putback(ch);
  token[count] = '\0';
}

void getStatements(ifstream &file)
{
string token,tmp;

tmp=Peek(file);
if (tmp=="}" || tmp==")") return;

	while (true)
	{
	file >> token;
	if (token=="}")
		{
		file.unget();
		return;
		}
	if (token=="var")
	getVarsDeclaration(file);	
		else
		{
		//token eh nome
		tmp=token;
		file >> token; // pega o segundo token depois do nome

		putback(token,file); // retorna ponteiro para o nome
		do file.putback(1); while (file.peek()==' ');
		putback(tmp,file); //retorna ponteiro para antes do token	
	
		if (token=="(")
			getFuncCall(file);

		cout << endl;
		}
	expect(";",file);
	}
}

void getVarsDeclaration(ifstream &file)
{ //var ja foi consumido
string token;
//----------------------------
file >> token; // "name?"
file.putback(token.length()); // retorna "name?"
if (token==";")
	{
	cout << "expected: variable identifier" <<endl;
	exit(0);
	}

while (token!=";" && file.good())
{
file >> token; // name
file >> token; // separador ou terminador
if (token!="," && token!=";")
	{
	cout << "expected: variable identifier separator or declaration terminator" <<endl;
	exit(0);
	}
file.unget(); //putback the ;	
}

}

ContractInfoRec::ContractInfoRec(ifstream &ifs, const char * const sf, int line):
	Record(ContractInfo, sf, line)
{
	ifs.get(Contract, sizeof(Contract));
	ContractLetter = Contract[0];

	char buf2[2+1];
	buf2[0] = Contract[1];
	buf2[1] = Contract[2];
	buf2[2] = '\0';
	BasePrice = atoi(buf2);
	
	buf2[0] = Contract[3];
	buf2[1] = Contract[4];
	SubLevel = atoi(buf2);

	char c;
	unsigned int i = 0;
	do {
		ifs.get(c);
		if (i < sizeof(Text)-2)
		{
			Text[i] = c;
			i++;
		}
	}
	while (c != '\n');

	if (Text[i-1] == '\n')
		Text[i-1] = '\0';
	else
		Text[i] = '\0';
	ifs.putback('\n');
}

bool eof(ifstream& in)
{
    char ch;
    in >> ch;
    in.putback(ch);
    return !in;
}

void skipspaces() {  
  char ch;  
  
  do {  
    ch = fin.get();  
  } while(isspace(ch));  
  fin.putback(ch);  
}

/*VARIABLES FUNCTION Define: READS AND STORES VARIABLES*/
string VARIABLES::Define(ifstream &Input) {
  //DECLARE LOCAL VARIABLES
  string Read_Next(ifstream &Input);
  string str;
  int i;
  char c;
  const int n = 7;
  int delim[n] = {9,10,13,32,44,61,124};/*{'\t','\n','?CR?',' ',',','=','|'}*/


  //GET VARIABLE NAME (WITHOUT LETTING Read_Next TRY TO REPLACE)
  str.clear();
  while (Input.get(c)) {
    //Check for comments
    if(int(c)=='%') {
      Input.ignore(10001, '\n');
      continue;
    }
    //Check for deliminators
    for(i=0;i<n;i++) {
      if(int(c)==delim[i]) {
        i=-1;
        break;
      }
    }
    if(i!=-1) {str += c;break;}
  }
  if(int(c)!='$') {
    //Not a valid variable name (return)
    Input.putback(c);
    return(Read_Next(Input));
  }
  str = Read_Next(Input);//NOTE: this allows deliminators between '$' and varaible name
  str.insert(0, "$");


  //FIND VARIABLE TO REDEFINE IT OR FIND UNUSED SLOT
  VARIABLES *var = this;
  while(var!=var->next) {
    if(str.compare(var->symb)==0) {break;}
    var = var->next;
  }


  //STORE SYMBOL AND VALUE
  var->symb = str;
  str = Read_Next(Input);
  i = int(str[0]);
  if( (i<43)||(i>57)||(i==44)||(i==47) ) {//Check if a number is present
    Log <<str<<" is not a valid expression for variable "<<var->symb<<endl;
    exit(0);
  }
  var->value = atof(str.c_str());
  if(var==var->next) {var->next = new VARIABLES();}//Allocate memory for next variable

  return(Define(Input));
}

char SaltarSeparadores (ifstream& f)
{
   char c;
   do {
      c= f.get();
   } while (isspace(c));
   f.putback(c);
   return c;
}

// push the file read pointer one step backward
void scanner::pushBackPointer(char ch)
{
    if(ch=='\n')
    {
        linenum--;
    }
    
    fin.putback(ch);
}

float getValeur(ifstream &fichier, char caractere)
{
    float temp = 0;

    fichier.putback(caractere);

    fichier>>temp;

    return temp;
}

void buildMap(ifstream& input, Map<string, Vector<char> >& _Map_, int& orderK) {
    char ch;
    while(input.get(ch)) {
		input.putback(ch);
        Vector<char> associatedValues; /* All the values associated with a key. */
        Vector<char> rewindValues; /* Holds chars to be put back into stream. */
        string newKey = "";

        /* Create a new key by appending as many letters as K value. */
        addToString(input, ch, newKey, rewindValues, orderK);

        /* Add to the key Map. */
        addToKey(_Map_, associatedValues, newKey, input);

        /* Put back the characters into ifstream from reverse. */
        for(int i=orderK-1; i>0; i--) {
            input.putback(rewindValues[i]);
        }
    }

}

int Term2(int inp)
{
  int result = inp;
  char a;
  testfile.get(a);
  if(a != EOF)
  {
    if (a == '*')
      result = Term2(result * Fact());
    else if (a == '/')
      result = Term2(result / Fact());
    else if (a == '+' || a == '-')
      testfile.putback(a);
  }
  return result;
}

// this is already inside the loop E'--> +TE'|-TE'| e
int Exp2(int input){
	
	int result = input;
	char a;
	if (!fin.eof() ){
		fin.get(a);
	//if( (a = fin.get()) != fin.eof()){ // just another way i could have written this. works for my notes.
		if (a == '+')
			result = Exp2(result + Term() );
		else if(a == '-')
			result = Exp2(result - Term() );
		else if(a == ')')
			fin.putback(a);
	}
	return result;
}

// T'--> *FT'| /FT'| e
int Term2(int input){
	
	int result = input;
	char a;

	//if( (a = fin.get()) != fin.eof() ){ // just another way i could have written this. works for my notes. 
	if (!fin.eof() ){
		fin.get(a);
		if (a == '*')
			result = Term2(result * Pwr() );
		else if (a == '/')
			result = Term2(result / Pwr() );
		else if (a == '+' || a == '-' || a == ')') // i added the ')' to close the parenthesis . it does this because when it finds it a gets put back so it knows what operation to do 
			fin.putback(a);
	}
	return result;
}