This question already has answers here:
Read whole ASCII file into C++ std::string [duplicate]
(9 answers)
Closed 9 years ago.
I have this function that reads the text from a file and adds it to a string, now the weird thing is that it works fine if its a short text. But if its a longer text the string becomes empty, any help solving this problem is appreciated.
string inlasning(string namn)
{
string filString, temp;
ifstream filen(namn.c_str());
if(!filen.good())
{
cout << "Otillganglig fil" << endl;
filString = "ERROR";
return filString;
}
else
{
while(!filen.eof())
getline(filen, temp);
filString.append(temp);
}
filen.close();
return filString;
}
1) Don't use eof() to control the loop. Put getline directly into the loop condition. Search StackOverflow if you have problems doing this.
2) Your while loop has no braces and thus only covers the getline line, despite your misleading indentation.
3) getline discards newlines. Your final string will be wrong.
4) The actual behavior you're observing comes from the fact that you only append the very last thing that getline returns to your string. When your file contains one line of text and doesn't end in a newline, this will seem to work. If it has more lines but doesn't end in a newline, you'll only get the last line. If the file does end in a newline, because of your incorrect loop condition the last call to getline will actually give you an empty string, which will be exactly the contents of your string.
Replace
while(!filen.eof())
getline(filen, temp);
filString.append(temp);
with
while(!filen.eof())
{
getline(filen, temp);
filString.append(temp);
}
Use "is_open()" to check if the file exists:
if( ! filen.is_open() ){...} // you don't need an else clause
...And your while loop must has braces or it will only execute the getline(...) instruction:
while( filen.good() ) {
getline( filen , temp );
filString += ( temp + '\n' );
}
If your file doesn't ends with '\n', remove the last char from the string
Related
This question already has answers here:
How do I read an entire file into a std::string in C++?
(23 answers)
Closed 3 years ago.
My function reads a file and puts it into a string in order for me to process it. I need to read just before EOF, obviously. The problem is that the EOF character is also put inside the string and I can't find a way to bypass it, since it leds other parts of the program to fail. I link the function below.
string name_to_open, ret = string();
ifstream in;
getline(cin, name_to_open);
in.open(name_to_open.c_str());
if (!in.is_open()) {
cout << "Error." << endl;
return string();
}
else {
ret += in.get();
while (in.good()) {
ret += in.get();
};
};
in.close();
return ret;
The function reads fine until the end of the file, then appends EOF and \0. How can I solve the problem? Does the EOF character work fine in controls? I also tried to put a line ret[ret.size() - 1] = '\0'; at the end of the cycle, but this doesn't seem to work either.
ret += in.get(); appends the character read from the tile to the string whether the value read was good or not. You need to 1) read, 2) test that the read is valid and the value read is safe to use, 3) use the value read. Currently your code reads, uses, and then tests whether or not the value read was safe to use.
Possible solution:
int temp;
while ((temp = in.get()) != EOF) // read and test. Enter if not EOF
{
ret += static_cast<char>(temp); // add the character
};
Note: get returns an int, not a char. This is to be able to insert out-of-band codes such as EOF without colliding with an existing valid character. Immediately treating the return value as a char could result in bugs because a special code may be mishandled.
Note: there are many better ways to read an entire file into a string: How do I read an entire file into a std::string in C++?
I'm trying to make a code which would change one given word from a file, and change it into another one. The program works in a way that it copies word by word, if it's normal word it just writes it into the output file, and if it's the one i need to change it writes the one i need to change to. However, I've enountered a problem. Program is not putting whitespaces where they are in the input file. I don't know the solution to this problem, and I have no idea if I can use noskipws since I wouldn't know where the file ends.
Please keep in mind I'm a complete newbie and I have no idea how things work. I don't know if the tags are visible enough, so I will mention again that I use C++
Since each reading of word is ended with either a whitespace or end of file, you could simply check whether the thing which stop your reading is end of file, or otherwise a whitespace:
if ( reached the end of file ) {
// What I have encountered is end of file
// My job is done
} else {
// What I have encountered is a whitespace
// I need to output a whitespace and back to work
}
And the problem here is how to check the eof(end of file).
Since you are using ifstream, things will be quite simple.
When a ifstream reach the end of file (all the meaningful data have been read), the ifstream::eof() function will return true.
Let's assume the ifstream instance that you have is called input.
if ( input.eof() == true ) {
// What I have encountered is end of file
// My job is done
} else {
// What I have encountered is a whitespace
// I need to output a whitespace and back to work
}
PS : ifstream::good() will return false when it reaches the eof or an error occurs. Checking whether input.good() == false instead can be a better choice here.
First I would advise you not to read and write in the same file (at least not during reading) because it will make your program much more difficult to write/read.
Second if you want to read all whitespaces easiest is to read whole line with getline().
Program that you can use for modifying words from one file to another could look something like following:
void read_file()
{
ifstream file_read;
ofstream file_write;
// File from which you read some text.
file_read.open ("read.txt");
// File in which you will save modified text.
file_write.open ("write.txt");
string line;
// Word that you look for to modify.
string word_to_modify = "something";
string word_new = "something_new";
// You need to look in every line from input file.
// getLine() goes from beginning of the file to the end.
while ( getline (file_read,line) ) {
unsigned index = line.find(word_to_modify);
// If there are one or more occurrence of target word.
while (index < line.length()) {
line.replace(index, word_to_modify.length(), word_new);
index = line.find(word_to_modify, index + word_new.length());
}
cout << line << '\n';
file_write << line + '\n';
}
file_read.close();
file_write.close();
}
This question already has answers here:
Reading from text file until EOF repeats last line [duplicate]
(7 answers)
Testing stream.good() or !stream.eof() reads last line twice [duplicate]
(3 answers)
reading a line in text file twice
(4 answers)
Closed 9 years ago.
I am trying to read values from a file to a vector
std::vector<float> setTimesArray (std::string flName){
int i=0, dummy=0;
float temp;
std::vector<float> pObs;
std::string line;
std::ifstream inFile;
inFile.open(flName.c_str());
if(!inFile){
std::cout<<"\n.obs file not valid. Quitting programme...";
exit(1);
}
while(inFile.good()){
i++;
getline(inFile, line);
if(i>=3){ //I don't want first two lines
std::istringstream in(line);
in>>dummy;//discards first value in the line
in>>temp;
pObs.push_back(temp);
in.str(""); //discards remaining part of the line
}
}
return pObs;
inFile.close();
}
Problem is, the last value gets repeated. For example, flName had total 975 lines. Thus pObs must be having size=973 (975-2 initial lines). But the size is 974 and I see that the last value is repeating. What mistake have I made?
try:
while (getline(inFile,line))
instead of while(inFile.good())
and remove the getline() call from within the method.
You may also want to change your last two lines of codes to this, as per Daniel Kamil Kozar's suggestion:
inFile.close();
return pObs;
After the last line, good() is still allowed to return true. It doesn't have to return false until after a failed read. Thus, if it returns true, and then fails the read, your line variable won't take a new value. The correct solution would probably be to correct the bounds checking, but in this case, moving the declaration of line into the scope of you while loop and checking for and empty string should correct the issue.
This question already has answers here:
What's preferred pattern for reading lines from a file in C++?
(5 answers)
Closed 9 years ago.
The code is:
ifstream fin("D://abc.txt", ios::in);
string line;
while ( fin ) {
getline( fin, line );
cout << line << endl;
}
The text file is:
hi, I am Eric!
hi, I am Jack!
And the output is
hi, I am Eric!
hi, I am Jack!
hi, I am Jack!
And when I change the condition to !fin.eof(), output is correct. Is eof a valid state of ifstream ?
It's because the state is not changed until after the std::getline function fails. This means that you read the first two lines correctly, but then the state isn't changed so you enter the loop again, but now the std::getline call fails but you don't check for it, and it's also now that the eof flag is set.
You should do e.g.
while (std::getline(...))
{
// ...
}
The eof state is only reached once you try reading past the end of the stream. The getline call that reads the last line from your file does not do so (it reads up until the newline). But the getline call in the next iteration of the loop will reach the end of the file.
A better way to read every line in the file is :
while (getline(fin, line)) {
cout << line << endl;
}
The usage
while(fin)
is not good. it will check the value of fin, not whether fin reaches the end.
you may check this page:
http://www.cplusplus.com/reference/string/string/getline/
when you finish the second call of function getline, the pointer fin not point to NULL, so you go into the third process in while, the third time you call
getline(fin,line);
it meet the eof of fin, so fin change state, then you won't go to the forth call, but since you didn't clear the value of
line
so it will also print
hi, I am Jack!
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Reading from text file until EOF repeats last line
The cout output from my c++ program, prints to console but overlaps.
For instance:
while(pFile.good()){
getline (pFile, pLine);
cout<<pLine;
}
This code, prints the last line, and some leftovers of the previous line.
I'm using vi on cygwin. This happened out of the blue. Did I change some setting?
getline() discards any newline character it encounters. To keep your code from merging all lines together into one big line, you need to do this instead:
cout << pLine << endl;
As chris pointed out, you also should use getline() as your while condition. Otherwise, the stream may be considered "good" now, but reach EOF when you call getline(). So try this loop:
while (getline(pFile, pLine)) {
cout << pLine << endl;
}
The reason your last line is printed twice is because your last call to getline() failed, but you still printed pLine (even though its content is undefined).
while(pFile.good()){
getline (pFile, pLine); // What happens if this line fails.
// Like when you read **past** the end of file.
cout<<pLine;
}
The correct version of your code is:
while(pFile.good()){
if (getline (pFile, pLine))
{ cout<<pLine;
}
}
But this is usually written as:
while(getline (pFile, pLine))
{
// The loop is only entered if the read worked.
cout<<pLine;
}
Remember that the last successful call to getline() reads up-to but not past the end of line. That mean the next call to getline() will fail and set the EOF bit.
Also note that your output is stinging together because you are not adding a '\n' seporator between your lines. Note: the getline() reads upto the next '\n' character but this termination character is not added to the string pLine.
here u are writing at sameline because getline simply discards new line character,thats why u have to write <<endl
while(pFile.good()){
getline (pFile, pLine);
cout<<pLine<<endl;
}