I know i'm making a stupid mistake somewhere and even though i've been reading old questions i'm unable to catch it. I'm hoping someone would point me in the right direction. As you can probably tell i'm new to C++.
#include <iostream>
#include <iomanip>
#include <string>
#include <fstream>
using namespace std;
int main()
{
//local variables
string answer, filePath, wordtest;
fstream openFile;
***stuff removed for space reasons***
cout << "Enter the full file path" << endl;
getline(cin, filePath);
openFile.open(filePath, ios::in); //Open file
while (openFile.peek() != EOF)
{
cin >> wordtest;
cout << wordtest;
//getline(cin, wordtest);
{
//wordCount = wordCount + 1;
}
}
openFile.close();
openFile.clear(std::ios_base::goodbit);
cout << "Loaded file and read " << wordCount << " words";
}
You are neither reading nor writing to openFile.
You need to use operator<< or operator>> with openFile.
Related
i want to receive an input from user and search a file for that input. when i found a line that includes that specific word, i want to print it and get another input to change a part of that line based on second user input with third user input. (I'm writing a hospital management app and this is a part of project that patients and edit their document).
i completed 90 percent of the project but i don't know how to replace it. check out following code:
#include <iostream>
#include <stream>
#include <string.h>
#include <string>
using namespace std;
int main(){
string srch;
string line;
fstream Myfile;
string word, replacement, name;
int counter;
Myfile.open("Patientlist.txt", ios::in|ios::out);
cout << "\nEnter your Name: ";
cin.ignore();
getline(cin, srch);
if(Myfile.is_open())
{
while(getline(Myfile, line)){
if (line.find(srch) != string::npos){
cout << "\nYour details are: \n" << line << endl << "What do you want to change? *type it's word and then type the replacement!*" << endl;
cin >> word >> replacement;
}
// i want to change in here
}
}else
{
cout << "\nSearch Failed... Patient not found!" << endl;
}
Myfile.close();
}
for example my file contains this line ( David , ha , 2002 ) and user wants to change 2002 to 2003
You cannot replace the string directly in the file. You have to:
Write to a temporary file what you read & changed.
Rename the original one (or delete it if you are sure everything went fine).
Rename the temporary file to the original one.
Ideally, the rename part should be done in one step. For instance, you do not want to end up with no file because the original file was deleted but the temporary one was not renamed due to some error - see your OS documentation for this.
Here's an idea:
#include <iostream>
#include <fstream>
#include <string>
#include <cstdio>
using namespace std;
void replace(string& s, const string& old_str, const string& new_str)
{
for (size_t off = 0, found_idx = s.find(old_str, off); found_idx != string::npos; off += new_str.length(), found_idx = s.find(old_str, off))
s.replace(found_idx, old_str.length(), new_str);
}
int main()
{
const char* in_fn = "c:/temp/in.txt";
const char* bak_fn = "c:/temp/in.bak";
const char* tmp_fn = "c:/temp/tmp.txt";
const char* out_fn = "c:/temp/out.txt";
string old_str{ "2002" };
string new_str{ "2003" };
// read, rename, write
{
ifstream in{ in_fn };
if (!in)
return -1; // could not open
ofstream tmp{ tmp_fn };
if (!tmp)
return -2; // could not open
string line;
while (getline(in, line))
{
replace(line, old_str, new_str);
tmp << line << endl;
}
} // in & tmp are closed here
// this should be done in one step
{
remove(bak_fn);
rename(in_fn, bak_fn);
remove(out_fn);
rename(tmp_fn, in_fn);
remove(tmp_fn);
}
return 0;
}
One possible way:
Close the file after you read it into "line" variable, then:
std::replace(0, line.length(), "2002", "2003")
Then overwrite the old file.
Note that std::replace is different from string::replace!!
The header is supposed to be <fstream> rather than <stream>
you can't read and write to a file simultaneously so I have closed the file after reading before reopening the file for writing.
instead of updating text inside the file, your line can be updated and then written to file.
#include <iostream>
#include <fstream>
#include <string.h>
#include <string>
using namespace std;
int main(){
string srch;
string line, line2;
fstream Myfile;
string word, replacement, name;
int counter;
Myfile.open("Patientlist.txt", ios::in);
cout << "\nEnter your Name: ";
cin.ignore();
getline(cin, srch);
if(Myfile.is_open())
{
while(getline(Myfile, line)){
if (line.find(srch) != string::npos){
cout << "\nYour details are: \n" << line << endl << "What do you want to change? *type it's word and then type the replacement!*" << endl;
cin >> word >> replacement;
int index = line.find(word);
if (index != string::npos){
Myfile.close();
Myfile.open("Patientlist.txt", ios::out);
line.replace(index, word.length(), replacement);
Myfile.write(line.data(), line.size());
Myfile.close();
}
}
// i want to change in here
}
}else
{
cout << "\nSearch Failed... Patient not found!" << endl;
}
}
I'm trying to learn about fstream and here is the code that I'm running on VS2019:
#include <iostream>
#include <iomanip>
#include <string>
#include <fstream>
using namespace std;
int main() {
//cout << "lOOKING IN FILE";
string s;
fstream dictionary("C:/Users/source/repos/Test2/Test2/Text.txt");
if (!dictionary) // were there any errors on opening?
exit(-1);
while (dictionary >> s) cout << s << '\n'; // Print all names in file
dictionary.seekp(0, ios::beg); // Go back to beginning of file
cout << dictionary.tellp() << endl;
dictionary >> s;
cout << s; // Print the first name
return 0;
}
The output is:
abc
acb
cab
-1
cab
Why does tellp give -1 and not go to beginning of file?
You need to clear the state of the stream.
Once the state of a stream have changed from good (i.e. when it reaches end-of-file or there's a failure) then you can't operate on the stream again without clearing the state.
I want to open a random .txt file and put the data into some strings.
It works if I write the path into the code.
I don't get it why this doesn't work.
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
string file;
ifstream filein(file.c_str());
cout << "Insert Path" << endl;
cin >> file;
cout << file << endl;
filein.open(file.c_str(), ios::in);
for (string line; getline(filein, line);) {
cout << line << endl;
}
return 0;
}
Your filename string is empty because std::string defaults to empty.
You are passing an empty string (or the nul string) to the ifstream constructor, which is at best, undefined behavior.
Try writing your code like this:
#include <iostream>
#include <fstream>
int main()
{
std::string file;
std::cout << "Insert Path" << std::endl;
std::getline(std::cin, file);
std::cout << file << std::endl;
std::ifstream filein(file);
for (std::string line; std::getline(filein, line); )
{
std::cout << line << std::endl;
}
return 0;
}
Notable edits include:
We're now constructing the ifstream object only when we need it, after file has had data stored, which means no more undefined behavior, and that we only attempt to open a file after we know what the path is.
We're retrieving a whole line when storing to file, instead of only the first word, which is crucial if your path includes any spaces.
We're just using the file string directly. There's no need to call c_str().
We're no longer using using namespace std;. There are many, many reasons why this is bad practice.
EDIT:
If you have a C++17-compliant compiler, I'm going to propose you write code that looks like this instead:
#include <iostream>
#include <fstream>
//You may need to write #include <experimental/filesystem>
#include <filesystem>
#include <string>
int main()
{
std::string input_line;
std::cout << "Insert Path" << std::endl;
std::getline(std::cin, input_line);
//You may need to write std::experimental::filesystem
std::filesystem::path file_path{input_line};
//This will print the "absolute path", which is more valuable for debugging purposes
std::cout << std::filesystem::absolute(file_path) << std::endl;
std::ifstream filein(file_path);
for (std::string line; std::getline(filein, line); )
{
cout << line << endl;
}
return 0;
}
Explicit use of path objects will make your code more readable and make errors more explicit, as well as grant you access to behavior you otherwise would not be able to access.
first what are you opening? as long as you string doesn't contain anything??
second even if the string contains a valid path and the opening was successfull at the first time but in the second will fail as long as you use the same file stream on multiple files without clearing its buffer and closing the previous file:
string file "C:\\MyProject\\data.txt"; // let's say a valid path
ifstream filein(file.c_str());
if(filein.fail()) // the condition fails as long as the opening was successfull
cout << "failed to open file!" << endl;
cout << "Insert Path" << endl;
cin >> file; // let's say the user enters a valid path again: "C:\\MyProject\\test.txt"
cout << file << endl;
filein.open(file.c_str(), ios::in); // fail to correct it:
filein.close();
filein.clear(); // very important
filein.open(file.c_str(), ios::in); // now it's ok!
for (string line; getline(filein, line);) {
cout << line << endl;
}
I wrote a quick C++ program that asks the user for a input text file and an output text file. The program is then supposed to number the lines in the file on the left margin. However, I cannot seem to get it working properly, it compiles fine but does not number the lines like it is supposed to. I believe it is a logical error on my part. I am also not too familiar with file i/o in C++ as I am just learning it now using old school textbooks.
Here is the file:
#include <iostream>
#include <fstream>
#include <string>
#include <cassert>
#include <cstdio>
using namespace std;
int main(void)
{int i = 0 , num = 1;
string inputFileName;
string outputFileName;
string s;
ifstream fileIn;
ofstream fileOut;
char ch;
cout<<"Enter name of input file: ";
cin>>inputFileName;
cout<<"Enter name of output file: ";
cin>>outputFileName;
fileIn.open(inputFileName.data());
fileOut.open(outputFileName.data());
assert(fileIn.is_open() );
assert(fileOut.is_open() );
while (!(fileIn.eof()))
{ch=fileIn.get();
if (ch=='\n') num++;
fileOut << num << "\n";
s.insert(i,1,ch); //insert character at position i
i++;
}
fileOut << s;
fileIn.close();
fileOut.close();
return 0;
}
If anyone could point me in thr right direction or give me some tips I would be eternally grateful.
int i = 0;
string line;
while (getline(infile, line))
{
outfile << (i++) << " " << line << "\n";
}
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main() {
fstream file("file.txt");
file << "this is new line" << endl;
file.flush();
string c;
file >> c;
cout << c << endl;
file.close();
}
when i run this output is empty, if i remove line file << "this is new line" << endl; I'm getting correct output, why ?
By writing to the file, you are moving the internal file pointer to the end of it. This means the the next time you read, you will be at the end of the file, and so nothing will be read.
Look at seek() for moving the file pointer.