I'm trying to write a very simple program that reads its standard input line by line (until "end" appears at the beginning of a line). At the same time, it tries to construct a new string that contains the concatenation of all the lines.
The behavior is quite puzzling. The lines are correctly read (as shown by the cout << current << endl line). However, the constructed string isn't what I expect. Instead, it contains only the last read. However, if I replace construct.append(current) by construct.append("foo"), it works perfectly fine.
What am I doing wrong here?
#include <iostream>
#include <string>
#include <cassert>
using namespace std;
int main() {
string construct;
while(true) {
string current;
getline(cin, current);
assert(!cin.eof());
if (current.find("end") == 0) { break; }
cout << current << endl;
construct.append(current);
}
cout << construct << endl;
return 0;
}
Compiled with:
g++ -o main main.cpp -Wall -std=c++0x
Input: input.txt
abcdef
ghij
end
Output: ./main < input.txt
abcdef
ghij
ghijef
If I type the input instead of using a file, it works as expected. Also I get the same result with gcc (linux) and clang (mac os).
I found the problem. My input file was an ascii file with CRLF line terminators (and I'm using a mac). The construct variable was created correctly, but it wasn't displayed properly by the terminal.
I copied the contents of my .txt file over to Word and deleted all of the hard returns, which worked, but that is not always ideal or possible. The character encoding did not seem to have an impact. What solved it is when I appended a line break as well as the string.
Text::Text(string file) {
ifstream in;
string line;
in.open( file.c_str() ); // because the file name is a parameter decided at runtime in my code
while(getline(in,line,'\n')){
fileContents.append(line+"\n"); // fixed by adding "\n" here
}
cout << "\n Final product:\n";
cout << fileContents;
}
Related
I have some code here
https://github.com/Fallauthy/Projects/blob/master/cPlusPlusProjects/bazaPracownikow/bazaPracownikow/bazaPracownikow/main.cpp
And I have no idea how to show contents in my file. I mean i know how, but it doesn't show same I Have in file (in link). It show in next line. This code is responsible to load file
while (!baseFile.eof()) {
//wczytaj zawartosc pliku do zmiennej
std::string buffer;
baseFile >> buffer;
//wypisz
loadLineFromBase += buffer;
loadLineFromBase += " \n";
}
std::cout << loadLineFromBase << std::endl;
Unless I see all your code all I can do for you is give you a sample in return, I don't know what you're trying to do but it seems in this case you're looking for this.
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
string Display = "";
ofstream FileOut;
ifstream FileInput;
FileOut.open("C:\\Example.txt");
FileOut << "This is some example text that will be written to the file!";
FileOut.close();
FileInput.open("C:\\Example.txt");
if (!FileInput)
{
cout << "Error File not Found: " << endl;
return 1;
}
while (!FileInput.eof())
{
getline(FileInput, Display);
}
FileInput.close();
cout << Display << endl;
return 0;
}
Simply put if you're currently working wit ha text document
use getline()
When you use getline() it takes two arguments the first will be in this case your ifstream object, as in what you're using to open the file. The second will be the string you're using to store the contents in.
Using the method I outlined above you'll be able to read the entire file contents.
And please next time as it was said above outline your problem more in depth and if you provide us with all of your code we may better assist you!
Your snippet of code automatically add a newline to every string read from the input file, even if originally those were words separeted by spaces. Probably you want to keep the structure of the original file, so it's better to read one line at a time and, unless you need it for some other uses, print it out in the same loop.
std::string buffer;
// read every line of baseFile till EOF
while ( std::getline(baseFile, buffer) ) {
std::cout << buffer << '\n';
}
I have some weird issues I cannot figure out. When I run the code below which takes a file.txt reads it line by line into a vector<string> and then compares each index to string "--" it does not make it to the comparison stage.
Further more, in the convert_file() under the for loop string m, has some weird behavior: string m = "1"; m+= "--"; ('--' inside vector) m+= "2"; will print to console 2--; which makes me think something is bugging out the vector. The 2 is replacing the 1, the first character. This makes it look like the vector is bugged.
#include <iostream>
#include <sstream>
#include <fstream>
#include <string>
#include <vector>
using namespace std;
vector<string> get_file(const char* file){
int SIZE=256, ln=0;
char str[SIZE];
vector<string> strs;
ifstream in(file, ios::in);
if(!in){
return strs;
} else {
while(in.getline(str,SIZE)){
strs.push_back(string(str));
ln++;
}
}
in.close();
return strs;
}
void convert_file(const char* file){
vector<string> s = get_file(file);
vector<string> d;
int a, b;
bool t = false;
string comp = "--";
for(int i=0; i<s.size(); i++){
string m = "1";
m+= string(s.at(i));
m+= "2";
cout << m << endl;
if(s.at(i) == comp){
cout << "s[i] == '--'" << endl;
}
}
}
int main(){
convert_file("test.txt");
return 0;
}
now when I run a test file to check a similar program:
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main(){
vector<string> s;
s.push_back("--");
s.push_back("a");
for(int i=0; i<s.size(); i++){
cout << "1" << s.at(i) << "2" << endl;
if(s.at(i) == "--"){
cout << i << "= --" << endl;
}
}
return 0;
}
prints off 1--2, 0= --, 1a2. it works, it prints properly, and does the comparison. This leads me to think something is happening when I pull the line into a string.
Windows 7, cygwin64
g++ version 4.9.3
compile: D:\projects\test>g++ -o a -std=c++11 test.cpp
Based on the behavior and the discussion the lines in the file are terminated using a "\r\n" sequence. The easiest approach for dealing with the remaining '\r' is to remove it after reading a line. For example:
for (std::string line; std::getline(file, line); ) {
if (!line.empty() && line.back() == '\r') {
line.resize(line.size() - 1u);
}
strs.push_back(line);
}
If you insist in reading into char arrays you can use file.gcount() to determine the number of characters read to find the end of the string quickly. Note, however, that the number includes the bewline character, i.e., you'd want to check str[file.gcount() - 2] and potentially set it to '\0' (if the count is bigger or equal to 2, of course).
As answered by Dietmar Kühl already, the problem is with the \r\n line endings.
However, you should not need to modify your source code. The default behaviour in C++ is supposed to be to open files in text mode. Text mode means that whenever a line ending is found, where "line ending" depends on the platform you're using, it gets translated so that your program just sees a single \n. You're supposed to explicitly request "binary mode" from your program to disable this line ending translation. This has been long-standing practise on Windows systems, is the behaviour well supported by the C++ standard, and is the expected behaviour with native Windows compilers, but for compatibility with POSIX and existing Unix programs that do not bother setting the file mode properly, Cygwin ignores this and defaults to opening files in binary mode unless a custom Cygwin-specific text mode is explicitly requested.
This is covered in the Cygwin FAQ. The first solutions provided there (using O_TEXT or "t", depending on how you open your file) are non-standard so break your code with other environments, and they are not as easy to use with C++ <fstream> file access.
However, the next solutions provided there do work even for C++ programs:
You can also avoid to change the source code at all by linking an additional object file to your executable. Cygwin provides various object files in the /usr/lib directory which, when linked to an executable, changes the default open modes of any file opened within the executed process itself. The files are
binmode.o - Open all files in binary mode.
textmode.o - Open all files in text mode.
textreadmode.o - Open all files opened for reading in text mode.
automode.o - Open all files opened for reading in text mode,
all files opened for writing in binary mode.
And indeed, changing your compiler and linker invocation from g++ -o a -std=c++11 test.cpp to g++ -o a -std=c++11 test.cpp /usr/lib/textmode.o, your program works without changes to your source code. Linking with textmode.o basically means that your I/O will work the way it already should work by default.
guys. I'm writing this small test program to read the text file from "EXAMPLE.txt" into my main program. At the output, I put "*" to displayed the data during the output is the data that I want to extract it out and locate into an array. Let say, in this test program the data that I wanted to extract is "JY9757AC", "AZ9107AC","GY9Z970C". But after that, I have did a try run and I faced this problem when comes to the output.
EXAMPLE.txt
ABC:JY9757AC
HDMI:AZ9107AC
SNOC:GY9Z970C
MAIN.CPP
main()
{
string output;
ifstream readExample;
readExample.open("EXAMPLE.txt");
while(readExample.eof())
{
getline(readExample,output,':');
cout << "* " << output <<endl;
}
}
OUTPUT
* ABC //while loop output the "ABC", which is the data that I don't want.
* JY9757AC
HDMI //it work's well, as what I expected and so and the SNOC below
* AZ9107AC
SNOC
* GY9Z970C
I have no any idea why is the "* ABC" is shown on the output, is there anything wrong with my logic. or I missed out something inside the while loop? Thank You in advance for helping to solve my code!
The delim parameter for getline replaces the default delimiter for new line which is "\n".
What you are currently getting as a "line" is:
ABC
JY9757AC\nHDMI
AZ9107AC\nSNOC
GY9Z970C
What you can do is more something like this (if your output like GY9Z970C) is fixed-size:
ssize_t len = getline(readExample,output,':');
cout << "* " << (char*)(output + (len - 8)) <<endl;
Output stores the first extraction from Example.txt and prints it followed by *. In the first iteration output = "ABC"; in the second iteration output = "JY9757AC";. I have added a getline() in the while loop that reads the unwanted part of the line. I also added a string[] to store the extracted values in.
#include <fstream>
#include <string>
using namespace std;
int main()
{
string output, notWanted, stringArray[3];
int i = 0;
ifstream readExample;
readExample.open("EXAMPLE.txt");
while (!readExample.eof())
{
getline(readExample, notWanted, ':');
getline(readExample, output);
cout << "* " << output << endl;
stringArray[i++] = output;
}
cin.get();
return 0;
}
First, I assume the while loop is while(!readExample.eof()), otherwise there should be no output at all.
Second, to your question, the first getline(readExample,output,':'); read "ABC" into the output, so at the next line it outputs * ABC, which is exactly what you got. No surprise.
I want to access specific lines in of text file to display or modify that one. My text file contains lines of different lengths and i heard cannot use seekg or seekp for such files. I got a code but it doesn't works. Can someone please tell me its fault of some other helpful idea?
#include <fstream>
#include <limits>
#include <string>
#include <iostream>
std::fstream& GotoLine(std::fstream& file, unsigned int num)
{
file.seekg(std::ios::beg);
for(unsigned int i=0; i < num - 1; ++i)
{
file.ignore(std::numeric_limits<std::streamsize>::max(),'\n');
}
return file;
}
int main()
{
using namespace std;
std::fstream& GotoLine(std::fstream& file, unsigned int num);
cout << "Starting..." << endl;
fstream file("bla.txt");
GotoLine(file, 8);
string line8;
file >> line8;
cout << "[" << line8 << "]" << endl;
// cin.get();
cout << "Finished..." << endl;
return 0;
}
string line8;
file >> line8;
will only extract until the first whitespace character is hit.
you could use something like:
string line8;
getline(file, line8);
This at least worked for me with the rest of your code on Windows 7 with VS2012
Standard C++11 (and earlier versions of the standard) dont have notion of lines contained inside files. Also POSIX (and even Windows or MacOSX) don't have it. Textual files usually contain lines of variable length (and only the line terminator is relevant, either \n or \r\n or \n\r, depending upon the operating system and perhaps the file read mode -binary or textual-).
In the 1960s or 1970s IBM mainframe OS/360 operating systems had "file" systems which did have files made of fixed-length lines, mimicking punched cards.
So, you have to read your file line by line and remember where are the line limits (or use std::istream::ignore to skip till \n).
Alternatively, read every line of your file into a std::vector<std::string> using std::getline on std::ifstream-s.
For /etc/fstab (or /proc/mounts) reading all the lines in a vector is a good idea, since it is always a tiny file. It usually have less than an few dozens of lines, often less than about a hundred char each. The pathological case could be a file with many thousand lines of comments, but that don't really happen in practice.
I've been trying to read some information in from a .txt file in C++ but it's not all working like I expect. Here is some example code:
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
char words[255];
int value = 0;
ifstream input_stream("test.txt");
input_stream >> value;
input_stream.getline(words, 256);
cout << value << endl;
cout << words << endl;
}
And test.txt contains:
1234
WordOne WordTwo
What I expect is for the code to print the two lines contained in the text file, but instead I just get:
1234
I've been reading about getline and istream but can't seem to find any solutions so any help would be appreciated.
Thanks
The newline character remains in the input stream after the read of the integer:
// Always check result to ensure variables correctly assigned a value.
if (input_stream >> value)
{
}
Then, the call to getline() reads the newline character and stops, producing an empty string. To correct, consume the newline character before calling getline() (options include using getline() or ignore()).
Note there is a version std::getline() that accepts a std::string as its argument to avoid using a fixed sized array of char, which is used incorrectly in the posted code.
ifstream's getline method gathers input until one of two options is hit. Either a terminating character or the size passed in is reached. In your case, the newline terminator is encountered before the size is reached.
Use another getline to retrieve the second line of text.
Reference
The problem you are seeing is that the first newline after 1234 is not consumed by input_stream>>(int); so the next getline only reads to the end of that file.
This is a very constructed scenario, commonly found in schoolwork. The more common scenario when reading a textfile is to consider the entire file as linebased text.
In this case the more convenient
string line;
while( std::getline( input_stream, line ) ){
}
is appropriate, and way less error prone.
The textfile would commonly have a predefined format. Perhaps name = value lines, and are parsed as such after the line is read from the file.
Here is a somewhat corrected version of your original code:
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
char words[256]; // was 255
int value = 0;
ifstream input_stream("test.txt");
input_stream >> value;
input_stream.ignore(); // skip '\n'
input_stream.getline(words, 256);
cout << value << endl;
cout << words << endl;
}
Also, I would advise you to use a string instead of a char[] and use the other getline function.