I want to find out the character length of each of the lines in a separate file, which is test.txt. test.txt contains two lines: the first contains hello, and the second is blank.
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
int main() {
ifstream inFile;
inFile.open("test.txt");
string currline;
while (getline(inFile, currline)) {
cout << currline.length() << endl;
}
}
When executing this program and inputting 'test.txt', I was expecting the output to be 5 0. However, the output was simply 5, which meant that the second line of test.txt was being ignored. How do I solve this issue without modifying the input file, or using a new modified file?
Your test.txt contains only one line - "hello" with a trailing '\n', rather than two lines.
Related
I want to be able to a string that contains certain characters in a file that contains one string per line.
#include <iostream>
#include <fstream>
#include <string>
int main(){
string line;
ifstream infile;
infile.open("words.txt");
while(getline(infile, line,' ')){
if(line.find('z')){
cout << line;
}
}
}
That's my attempt at finding all the string that contains the character z.
The text file contains random strings such as
fhwaofhz
cbnooeht
rhowhrj
perwqreh
dsladsap
zpuaszu
so with my implementation, it should only print out the strings with the character z in it. However, it seems to be reprinting out all the contents from the text file again.
Problem:
In your file the strings aren't separated by a space (' ') which is the end delimiter, they are separated by a end of line ('\n'), that is a different character. As a consequence, in the first getline everything goes to line. line contains all the text in the file, including z's, so all the content is printed. Finally, the code exits the while block after running once because getline reaches the end of the file and fails.
If you run this code
#include <iostream>
#include <fstream>
#include <string>
int main(){
std::string line;
std::ifstream infile;
infile.open("words.txt");
while(getline(infile, line,' ')){
std::cout << "Hi";
if(line.find('z')){
std::cout << line;
}
}
}
"Hi" will be only printed once. That is because the while block is only executed once.
Additionaly, see that line.find('z') won't return 0 if not match is found, it will return npos. See it running this code (As it says here):
#include <iostream>
#include <fstream>
#include <string>
int main(){
std::string line;
std::ifstream infile;
infile.open("words.txt");
while(getline(infile,line)){
std::cout << line.find('z');
if(line.find('z')){
std::cout << line << "\n";
}
}
}
Solution:
Use getline(infile,line) that is more suitable for this case and replace if(line.find('z')) with if(line.find('z') != line.npos).
while(getline(infile,line)){
if(line.find('z') != line.npos){
std::cout << line << "\n";
}
}
If you need to put more than one string per line you can use the operator >> of ifstream.
Additional information:
Note that the code you posted won't compile because string, cout and ifstream are in the namespace std. Probably it was a part of a longer file where you were using using namespace std;. If that is the case, consider that it is a bad practice (More info here).
Full code:
#include <iostream>
#include <fstream>
#include <string>
int main(){
std::string line;
std::ifstream infile;
infile.open("words.txt");
while(getline(infile,line)){
if(line.find('z') != line.npos){
std::cout << line << "\n";
}
}
}
getline extracts characters from the source and stores them into the variable line until the delimitation character is found. Your delimiter character is a space (" "), which isn't present in the file, so line will contain the whole file.
Try getline(infile, line, '\n') or simply getline(infile, line) instead.
The method find returns the index of the found character, where 0 is a perfectly valid index. If the character is not found, it returns npos. This is a special value whcih indicates "not found", and it's nonzero to allow 0 to refer to a valid index. So the correct check is:
if (line.find('z') != string::npos)
{
// found
}
I want get from user word and put into place in file where is certian word.
I have problem with getline.
In new file I don't have any new line.
When I add Newline to string which I write to file, this line is read two times and writeto file to times (I think that bcoz I saw this newfile)
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
string contain_of_file,bufor,word,empty=" ",new_line="\n";
string conection;
string::size_type position;
cout<<"Give a word";
cin>>word;
ifstream NewFile;
ofstream Nowy1;
Nowy1.open("tekstpa.txt", ios::app);
NewFile.open("plik1.txt");
while(NewFile.good())
{
getline(NewFile, contain_of_file);
cout<<contain_of_file;
position=contain_of_file.find("Zuzia");
if(position!=string::npos)
{
conection=contain_of_file+empty+word+new_line;
Nowy1<<conection;
}
Nowy1<<contain_of_file;
}
Nowy1.close();
NewFile.close();
cin.get();
return 0;
}
The problem here is not your reading. directly, but about your loop.
Do not loop while (stream.good()) or while (!stream.eof()). This is because the eofbit flag is not set until after you try to read from beyond the file. This means that the loop will iterate one extra time, and you try to read from the file but the std::getline call will fails but you don't notice it and just continue as if nothing happened.
Instead do
while (std::getline(NewFile, contain_of_file)) { ... }
And an unrelated tip: The variable conection is not needed, you can instead do just
Nowy1 << contain_of_file << ' ' << word << '\n';
So I am trying to read from a file named input_file till it reaches the end. I've tried using while (!input_file.eof()) but it goes on for an infinite loop. I looked around on the forum and tried using while (getline(input_file, line)) but that just returns an empty line. I'm not using both getline() and the >> operator like other questions were.
How do I get around this? Here's my code:
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
// Main program
void CalfFlac(ifstream& input_file) {
string text;
string line;
while (getline(input_file, line)) {
text += line;
}
cout << text << endl;
}
int main() {
ifstream input_file;
input_file.open("calfflac.in");
CalfFlac(input_file);
}
input_file contains a single line Confucius say: Madam, I'm Adam. followed by a carriage return.
Thanks for the help!
PS: I'd prefer if the solution remained simple, as this appears to be a pretty simple problem.
EDIT: Make sure you have the right file name! I tried a bogus file name and it printed a blank line as your describe.
I tried your code with a correct file name and it worked for me
In main add this line:
int main() {
ifstream input_file;
input_file.open("calfflac.in");
if(!input_file)
cout << "File path is wrong!";
CalfFlac(input_file);
}
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.
I'm new to C++, and I'm trying to write a short C++ program that reads lines of
text from a file, with each line containing one integer key and one alphanumeric string value (no embedded whitespace). The number of lines is not known in advance, (i.e., keep reading lines until end of file is reached). The program needs to use the 'std::map' data structure to store integers and strings read from input (and to associate integers with strings). The program then needs to output string values (but not integer values) to standard output, 1 per line, sorted by integer key values (smallest to largest). So, for example, suppose I have a text file called "data.txt" which contains the following three lines:
10 dog
-50 horse
0 cat
-12 zebra
14 walrus
The output should then be:
horse
zebra
cat
dog
walrus
I've pasted below the progress I've made so far on my C++ program:
#include <fstream>
#include <iostream>
#include <map>
using namespace std;
using std::map;
int main ()
{
string name;
signed int value;
ifstream myfile ("data.txt");
while (! myfile.eof() )
{
getline(myfile,name,'\n');
myfile >> value >> name;
cout << name << endl;
}
return 0;
myfile.close();
}
Unfortunately, this produces the following incorrect output:
horse
cat
zebra
walrus
If anyone has any tips, hints, suggestions, etc. on changes and revisions
I need to make to the program to get it to work as needed, can you please
let me know?
Thanks!
See it:
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
int main()
{
string name;
int value;
ifstream myfile("text.txt", ifstream::in);
while(myfile >> value >> name)
cout << name << endl;
return 0;
}
You are having problems because you attempt to read each line twice: first with getline and then with operator>>.
You haven't actually used std::map in any regard, at all. You need to insert the integer/string pair into the map, and then iterate over it as the output. And there's no need to close() the stream.
Instead of using "! myfile.eof()" use this code it will help.
ifstream is;
string srg;
is.open(filename);
while(getline(is,srg))
{//your code
}