I'm having some trouble with detecting two '//' as a char and then deleting from the first '/' till the end of the line (im guessing /n comes into use here).
{
ifstream infile;
char comment = '//';
infile.open("test3.cpp");
if (!infile)
{
cout << "Can't open input file\n";
exit(1);
}
char line;
while (!infile.eof())
{
infile.get(line);
if (line == comment)
{
cout << "found it" << endl;
}
}
return 0;
}
In the test3.cpp file there are three comments, so 3 lots of '//'. But I can't detect the double slash and can only detect a single / which will affect other parts of the c++ file as I only want to delete from the beginning of a comment to the end of the line?
I'm having some trouble with detecting two '//' as a char
That's because // is not a character. It is a sequence of two characters. A sequence of characters is known as a string. You can make string literals with double quotation marks: "//".
A simple solution is to compare the current input character from the stream to the first character of the string "//" which is '/'. If it matches, then compare the next character from the stream with the second character in the string that is searched for. If you find two '/' in a row, you have your match. Or you could be smart and read the entire line into a std::string and use the member functions to find it.
Also:
while (!infile.eof())
{
infile.get(line);
// using line without testing eof- and badbit
This piece of code is wrong. You test for eofbit before reading the stream and process the input.
And your choice of name for the line variable is a bit confusing since it doesn't contain the entire. line but just one character.
Related
I am trying to write a code that will read in c++ files, recognize comments, and store each words in comment into a vector. My problem is that I cannot find a way to read in a single line comment.
My logic is this: If the first character in a string buffer is '/' check for second char to determine whether it is a single line or multi-line comments. If the comment is single line, read in every word delimited by whitespace until I hit new line character '\n'. If the comment is multi-line, I will read in every word until I hit another */. so the code snippet for this is,
while(!input.eof())
{
string buffer;
input >> buffer;
//check if the line is comment
if(buffer[0] == '/')
{
//single line comment
if(buffer[1] == '/')
{
//read in until I hit newlineChar, and store all words into vector
while(buffer[0] != '\n')
{
input >> buffer;
vector.add(buffer);
}
}
//multiline comment
else if(buffer[1] == '*')
{
//read until I hit */ and store all words into vector
while(buffer[buffer.size()-1] != '*' && buffer[buffer.size()] != '/')
{
input >> buffer;
vector.add(buffer);
}
}
}
}
The Problem is with my understanding of new line character. I don't quite understand how string processes the new line char. I'm assuming the string treats new line char as another delimiter just like whitespace. But even in such case, there has to be a way to recognize end of a line using string. What could be a solution to this? Any input is appreciated.
EDIT: Taking advice of user4581301, I added the while loop that reads till the end of file. And to note the problem of lines having extraction operator followed by // like
std::cout<<"//this is not a comment.";
And one way I can think of to avoid this is to read in entire line using getline and char*.
char buffer[200];
input.getline(buffer,200);
string tempStr = buffer;
vector.add(tempStr);
In this case, how can I break individual string stored in vector into words?
C++ ifstream get line change getline output from char to string
I got a text file.. so i read it and i do something like
char data[50];
readFile.open(filename.c_str());
while(readFile.good())
{
readFile.getline(data,50,',');
cout << data << endl;
}
My question is instead of creating a char with size 50 by the variable name data, can i get the getline to a string instead something like
string myData;
readFile.getline(myData,',');
My text file is something like this
Line2D, [3,2]
Line3D, [7,2,3]
I tried and the compiler say..
no matching function for getline(std::string&,char)
so is it possible to still break by delimiter, assign value to a string instead of a char.
Updates:
Using
while (std::getline(readFile, line))
{
std::cout << line << std::endl;
}
IT read line by line, but i wanna break the string into several delimiter, originally if using char i will specify the delimiter as the 3rd element which is
readFile.getline(data,50,',');
how do i do with string if i break /explode with delimiter comma , the one above. in line by line
Use std::getline():
std::string line;
while (std::getline(readFile, line, ','))
{
std::cout << line << std::endl;
}
Always check the result of read operations immediately otherwise the code will attempt to process the result of a failed read, as is the case with the posted code.
Though it is possible to specify a different delimiter in getline() it could mistakenly process two invalid lines as a single valid line. Recommend retrieving each line in full and then split the line. A useful utility for splitting lines is boost::split().
string numbers;
string fileName = "text.txt";
ifstream inputFile;
inputFile.open(fileName.c_str(),ios_base::in);
inputFile >> numbers;
inputFile.close();
cout << numbers;
And my text.txt file is:
1 2 3 4 5
basically a set of integers separated by tabs.
The problem is the program only reads the first integer in the text.txt file and ignores the rest for some reason. If I remove the tabs between the integers it works fine, but with tabs between them, it won't work. What causes this? As far as I know it should ignore any white space characters or am I mistaken? If so is there a better way to get each of these numbers from the text file?
When reading formatted strings the input operator starts with ignoring leading whitespace. Then it reads non-whitespace characters up to the first space and stops. The non-whitespace characters get stored in the std::string. If there are only whitespace characters before the stream reaches end of file (or some error for that matter), reading fails. Thus, your program reads one "word" (in this case a number) and stops reading.
Unfortunately, you only said what you are doing and what the problems are with your approach (where you problem description failed to cover the case where reading the input fails in the first place). Here are a few things you might want to try:
If you want to read multiple words, you can do so, e.g., by reading all words:
std::vector<std::string> words;
std::copy(std::istream_iterator<std::string>(inputFile),
std::istream_iterator<std::string>(),
std::back_inserter(words));
This will read all words from inputFile and store them as a sequence of std::strings in the vector words. Since you file contains numbers you might want to replace std::string by int to read numbers in a readily accessible form.
If you want to read a line rather than a word you can use std::getline() instead:
if (std::getline(inputFile, line)) { ... }
If you want to read multiple lines, you'd put this operation into a loop: There is, unfortunately, no read-made approach to read a sequence of lines as there is for words.
If you want to read the entire file, not just the first line, into a file, you can also use std::getline() but you'd need to know about one character value which doesn't occur in your file, e.g., the null value:
if (std::getline(inputFile, text, char()) { ... }
This approach considers a "line" a sequence of characters up to a null character. You can use any other character value as well. If you can't be sure about the character values, you can read an entire file using std::string's constructor taking iterators:
std::string text((std::istreambuf_iterator<char>(inputFile)),
std::istreambuf_iterator<char>());
Note, that the extra pair of parenthesis around the first parameter is, unfortunately, necessary (if you are using C++ 2011 you can avoid them by using braces, instead of parenthesis).
Use getline to do the reading.
string numbers;
if (inputFile.is_open())//checking if open
{
getline (inputFile,numbers); //fetches entire line into string numbers
inputFile.close();
}
Your program does behave exactly as in your description : inputFile >> numbers; just extract the first integer in the input file, so if you suppress the tab, inputFile>> will extract the number 12345, not 5 five numbers [1,2,3,4,5].
a better method :
vector< int > numbers;
string fileName = "text.txt";
ifstream inputFile;
inputFile.open(fileName.c_str(),ios_base::in);
char c;
while (inputFile.good()) // loop while extraction from file is possible
{
c = inputFile.get(); // get character from file
if ( inputFile.good() and c!= '\t' and c!=' ' ) // not sure of tab and space encoding in C++
{
numbers.push_back( (int) c);
}
}
inputFile.close();
I am trying to read a file line by line using the code below :
void main()
{
cout << "b";
getGrades("C:\Users\TOUCHMATE\Documents\VS projects\GradeSystem\input.txt");
}
void getGrades(string file){
string buf;
string line;
ifstream in(file);
if (in.fail())
{
cout << "Input file error !!!\n";
return;
}
while(getline(in, line))
{
cout << "read : " << buf << "\n";
}
}
For some reason it keeps returning "input file error!!!". I have tried to full path and relative path (by just using the name of the file as its located in the same folder as the project). what am I doing wrong?
You did not escape the string. Try to change with:
getGrades("C:\\Users\\TOUCHMATE\\Documents\\VS projects\\GradeSystem\\input.txt");
otherwise all the \something are misinterpreted.
As Felice said the '\' is an escape. Thus you need two.
Or you can use the '/' character.
As windows has accepted this as a directory separator for a decade or more now.
getGrades("C:/Users/TOUCHMATE/Documents/VS projects/GradeSystem/input.txt");
This has the advantage that it looks much neater.
first, if you wanna say '\' in a string, you should put '\\', that's the path issue.
then, the string buf is not in connect to your file..
The backslash in C strings is used for escape sequences (e.g. \n is newline, \r carriage return, \t is a tabulation, ...), thus your string is getting garbled because for each backslash+character sequence the compiler is replacing the corresponding escape sequence. To enter backslashes in a C string you have to escape them, using \\:
getGrades("C:\\Users\\TOUCHMATE\\Documents\\VS projects\\GradeSystem\\input.txt");
By the way, it's int main, not void main, and you should return an exit code (usually 0 if everything went fine).
once again I ask for help. I haven't coded anything for sometime!
Now I have a text file filled with random gibberish. I already have a basic idea on how I will count the number of occurrences per word.
What really stumps me is how I will determine what line the word is in. Gut instinct tells me to look for the newline character at the end of each line. However I have to do this while going through the text file the first time right? Since if I do it afterwords it will do no good.
I already am getting the words via the following code:
vector<string> words;
string currentWord;
while(!inputFile.eof())
{
inputFile >> currentWord;
words.push_back(currentWord);
}
This is for a text file with no set structure. Using the above code gives me a nice little(big) vector of words, but it doesn't give me the line they occur in.
Would I have to get the entire line, then process it into words to make this possible?
Use a std::map<std::string, int> to count the word occurrences -- the int is the number of times it exists.
If you need like by line input, use std::getline(std::istream&, std::string&), like this:
std::vector<std::string> lines;
std::ifstream file(...) //Fill in accordingly.
std::string currentLine;
while(std::getline(file, currentLine))
lines.push_back(currentLine);
You can split a line apart by putting it into an std::istringstream first and then using operator>>. (Alternately, you could cobble up some sort of splitter using std::find and other algorithmic primitaves)
EDIT: This is the same thing as in #dash-tom-bang's answer, but modified to be correct with respect to error handing:
vector<string> words;
int currentLine = 1; // or 0, however you wish to count...
string line;
while (getline(inputFile, line))
{
istringstream inputString(line);
string word;
while (inputString >> word)
words.push_back(pair(word, currentLine));
}
Short and sweet.
vector< map< string, size_t > > line_word_counts;
string line, word;
while ( getline( cin, line ) ) {
line_word_counts.push_back();
map< string, size_t > &word_counts = line_word_counts.back();
istringstream line_is( line );
while ( is >> word ) ++ word_counts[ word ];
}
cout << "'Hello' appears on line 5 " << line_word_counts[5-1]["Hello"]
<< " times\n";
You're going to have to abandon reading into strings, because operator >>(istream&, string&) discards white space and the contents of the white space (== '\n' or != '\n', that is the question...) is what will give you line numbers.
This is where OOP can save the day. You need to write a class to act as a "front end" for reading from the file. Its job will be to buffer data from the file, and return words one at a time to the caller.
Internally, the class needs to read data from the file a block (say, 4096 bytes) at a time. Then a string GetWord() (yes, returning by value here is good) method will:
First, read any white space characters, taking care to increment the object's lineNumber member every time it hits a \n.
Then read non-whitespace characters, putting them into the string object you'll be returning.
If it runs out of stuff to read, read the next block and continue.
If the you hit the end of file, the string you have is the whole word (which may be empty) and should be returned.
If the function returns an empty string, that tells the caller that the end of file has been reached. (Files usually end with whitespace characters, so reading whitespace characters cannot imply that there will be a word later on.)
Then you can call this method at the same place in your code as your cin >> line and the rest of the code doesn't need to know the details of your block buffering.
An alternative approach is to read things a line at a time, but all the read functions that would work for you require you to create a fixed-size buffer to read into beforehand, and if the line is longer than that buffer, you have to deal with it somehow. It could get more complicated than the class I described.