How do you alternate between reading char and int in C plus plus from a text file?

Answer 1

Text files do not contain int types, only char types. Alternating between the two when reading a text file is an exercise in futility.

The assumption here is that the text file contains integers in string form. To extract the integers you must convert the digits into values. The digit '4' is not a number; four is the number, 4 is just the symbol for the number four. However, '4' is ASCII character code 52, thus if we subtract 48 we get its value. Character '0' is ASCII 48, thus subtracting '0' is the same as subtracting 48. If 0 <= value <= 9, then we know the character is a digit.

The following example demonstrates how to extract integers from strings. The code can be easily adapted to extract integers from text files.

#include <iostream>

int main()

{

char str[] = "This is a string that has 54 characters and 2 numbers.";

std::cout << "'" << str << "'\n" << std::endl;

int idx = 0;

again:

int number = 0;

while( str[idx] )

{

char value = str[idx++] - '0';

if( value >= 0 && value <= 9 )

{

number *= 10;

number += value;

}

else if( number )

break;

}

if( number )

std::cout << "The number " << number << " was found in the string." << std::endl;

if( str[idx] )

goto again;

return( 0 );

}

Output:

'This is a string that has 54 characters and 2 numbers.'

The number 54 was found in the string.

The number 2 was found in the string.

Answer 2

#include<iostream>

#include<fstream>

#include<string>

std::string load_text( std::ifstream& in )

{

std::string result;

// we'll read 4k at a time

const size_t bufsize = 4096;

// intialise a buffer (include a null-terminator)

char buffer[bufsize+1];

memset( buffer, 0, bufsize+1 );

while( in.good() )

{

// read characters

in.read( buffer, bufsize );

// append to result

result.append( buffer );

// reset buffer for next read

memset( buffer, 0, bufsize );

}

return( result );

}

int main ()

{

// assign a filename to an input file stream

std::ifstream in( "c:\\readme.txt" );

// ensure the file is good

if( in.bad() )

return( -1 );

// load the text into a string

std::string str = load_text( in );

// finished with file

in.close();

// output the string

std::cout << str.c_str() << std::endl;

}

Answer 3

Here is a simple program that saves the contents of a file to a string:

#include <iostream>

#include <fstream>

#include <string>

using namespace std;

void main()

{

string VariableName;

ifstream infile;

infile.open("TextFileHere.txt");

while(!infile.eof) //Gets all the lines

{

getline(infile,VariableName); //Saves the string to the variable

cout << VariableName; //Outputs the variable to the console

}

infile.close();

system("pause");

}

Answer 4

Use an input file stream (ifstream) object to read a text file.