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Oct 22nd, 2008

Reading in new line character from a file.

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Hi, I'm trying to read a series of ascii characters from a text file as their corresponding decimal integers. However when I try to read in the # 26 it is read in as a # 10 and no further characters after this are read. I've found out that # 26 represents a substitution character and # 10 is a new line (http://www.asciitable.com/)

This is the code I'm using to illustrate my problem;

c++ Syntax (Toggle Plain Text)
 
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
using namespace std;
int main()
{
	// fill up the vector with 4 integers
	vector <int> vec;
	vec.push_back(21);
	vec.push_back(23);
	vec.push_back(26);
	vec.push_back(29);
	cout << "Numbers in vector are:" << endl;
	for (int i = 0; i < vec.size(); i++) {
		cout << vec[i] << " ";
	}
	//write out the vector contents as chars to a text file
	ofstream outfile("test.txt");
	if (outfile.fail()) {
		cout << "test.txt"
		<< endl;
		return 1;
	}
	for (int g = 0; g < vec.size(); g++) {
		outfile << char(vec[g]);
	}
	outfile.close();
	//now read the chars back in as the ints [21, 23, 26, 29]
	string str, tmp;
	ifstream infile("test.txt");
	if (infile.fail()) {
		cout << "Error opening test.txt"
		<< endl;
		return 1;
	}
	while (!infile.eof()) {
		getline(infile, tmp);
		str += tmp;
		str += "\n";
	}
	infile.close();
	cout << endl << "String read in is:" <<endl;
	for (int g=0; g<str.size(); g++) {
		cout << int(str[g]) << " ";
	}
	cout << endl;
}
 
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
using namespace std;
int main()
{
	// fill up the vector with 4 integers
	vector <int> vec;
	vec.push_back(21);
	vec.push_back(23);
	vec.push_back(26);
	vec.push_back(29);
	cout << "Numbers in vector are:" << endl;
	for (int i = 0; i < vec.size(); i++) {
		cout << vec[i] << " ";
	}
	//write out the vector contents as chars to a text file
	ofstream outfile("test.txt");
	if (outfile.fail()) {
		cout << "test.txt"
		<< endl;
		return 1;
	}
	for (int g = 0; g < vec.size(); g++) {
		outfile << char(vec[g]);
	}
	outfile.close();
	//now read the chars back in as the ints [21, 23, 26, 29]
	string str, tmp;
	ifstream infile("test.txt");
	if (infile.fail()) {
		cout << "Error opening test.txt"
		<< endl;
		return 1;
	}
	while (!infile.eof()) {
		getline(infile, tmp);
		str += tmp;
		str += "\n";
	}
	infile.close();
	cout << endl << "String read in is:" <<endl;
	for (int g=0; g<str.size(); g++) {
		cout << int(str[g]) << " ";
	}
	cout << endl;
}

Any ideas what I can do?

Thankyou for any reply.

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sarah_ella

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Oct 22nd, 2008

Re: Reading in new line character from a file.

The input file is opened in text mode, which means your program will never see the '\n' character(s) because getline() will filter it out, leaving only the characters up to but not including '\n'.

That read loop is wrong anyway because eof() doesn't work that way.

C++ Syntax (Toggle Plain Text)
	while (getline(infile, tmp)) {
		str += tmp;
		str += "\n";
	}
	while (getline(infile, tmp)) {
		str += tmp;
		str += "\n";
	}

I don't know what you mean by reading # 26. Does that file contain binary information? If yes, then it isn't a text file.

Last edited by Ancient Dragon; Oct 22nd, 2008 at 7:05 am.

Ancient Dragon

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Oct 22nd, 2008

Re: Reading in new line character from a file.

It isn't the number 26, its the ascii character that has a decimal value 26. This is written to a text file but is read back as the decimal value 10.

sarah_ella

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Oct 22nd, 2008

Re: Reading in new line character from a file.

test.txt is a binary file, not a text file so getline() doesn't know how to read it. Then you are putting all that binary stuff into a std::string and ucing cout to display it -- cout can't because it doesn't know how to display binary data when converted to char.

Use a hex editor on that test.txt file and it contains the 4 values that were written.

Maybe this is what you want?

C++ Syntax (Toggle Plain Text)
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <sstream>
using namespace std;
int main()
{
	// fill up the vector with 4 integers
	vector <int> vec;
	vec.push_back(21);
	vec.push_back(23);
	vec.push_back(26);
	vec.push_back(29);
	cout << "Numbers in vector are:" << endl;
	for (size_t i = 0; i < vec.size(); i++) {
		cout << vec[i] << " ";
	}
	//write out the vector contents as chars to a text file
	ofstream outfile("test.txt");
	if (outfile.fail()) {
		cout << "test.txt"
		<< endl;
		return 1;
	}
	for (size_t g = 0; g < vec.size(); g++) {
		outfile << char(vec[g]);
	}
	outfile.close();
    vec.erase(vec.begin(),vec.end());
	//now read the chars back in as the ints [21, 23, 26, 29]
    ifstream infile("test.txt", ios::binary);
	if (infile.fail()) {
		cout << "Error opening test.txt"
		<< endl;
		return 1;
	}
    char c;
    std::string str;
	while (infile.good()) {
        c = infile.get();
        std::stringstream sstm;
        sstm << c;
        str += sstm.str();
	}
    infile.close();
	cout << endl << "String read in is:" <<endl;
	for (size_t g=0; g<str.size(); g++) {
		cout << int(str[g]) << " ";
	}
	cout << endl;
}
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <sstream>
using namespace std;
int main()
{
	// fill up the vector with 4 integers
	vector <int> vec;
	vec.push_back(21);
	vec.push_back(23);
	vec.push_back(26);
	vec.push_back(29);
	cout << "Numbers in vector are:" << endl;
	for (size_t i = 0; i < vec.size(); i++) {
		cout << vec[i] << " ";
	}
	//write out the vector contents as chars to a text file
	ofstream outfile("test.txt");
	if (outfile.fail()) {
		cout << "test.txt"
		<< endl;
		return 1;
	}
	for (size_t g = 0; g < vec.size(); g++) {
		outfile << char(vec[g]);
	}
	outfile.close();
    vec.erase(vec.begin(),vec.end());
	//now read the chars back in as the ints [21, 23, 26, 29]
    ifstream infile("test.txt", ios::binary);
	if (infile.fail()) {
		cout << "Error opening test.txt"
		<< endl;
		return 1;
	}
    char c;
    std::string str;
	while (infile.good()) {
        c = infile.get();
        std::stringstream sstm;
        sstm << c;
        str += sstm.str();
	}
    infile.close();
	cout << endl << "String read in is:" <<endl;
	for (size_t g=0; g<str.size(); g++) {
		cout << int(str[g]) << " ";
	}
	cout << endl;
}

Ancient Dragon

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Oct 22nd, 2008

Re: Reading in new line character from a file.

Ah, thanks, I understand now

sarah_ella

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