Is it possible to edit text in a file using cpp code. Already there is related question on it, but it doesn't solve my problem. Kindly help me out.
I have given a rough code line on this.
seek() through the file and try to replace the contents with new string from that point till the end of line.
I need the "hello" string be placed and must be the end of line.
like if we have new.txt as
ABCDEFGHIJKLMNOPQRST
If I want the file content to be changed as
ABCDEHELLO
I am getting the file content as
ABCDHELLOJKLMNOPQRST
fstream file("new.txt",fstream::in|fstream::out);
file.open();
while(getline(file,str))
{
if(value==strstr())
{
file.seekp(pos);
str.erase(pos,len);//len specifies the value till end of str
str.replace(pos,6,"hello");
char *d=new char[str.length()+1];
strcpy(d,str.c_str());
file.write(d,strlen(d));
delete [] d;
}
}
If I could copy the file contents to the string, manipulate it, then copy to the new file then it is possible.
Is it possible to change the contents in the same file. If so kindly help me out, I am struck in this. If the replacing string is longer than the one actually existing then this works, but if the replacing string is smaller than the one which is actually existing then I am unable to do.
if you case is only one line in the file you can easily separate the I/O process in two stages. Read the file and get the position of the text. then close the file and reopened as out then write the string you want. Note that this will work if you have one line in the file
check the following code
std::string value = "GFGHHFGHH";
std::string str;
std::fstream file("new.txt", std::ios::in);
std::size_t found;
while (file >> str)
{
found = str.find(value);
if (found != std::string::npos)
{
str.erase(value.length() );
str.replace(found, 6, "hello");
}
}
file.close();
file.open("new.txt", std::ios::out);
file << str;
file.close();
You can do it using system call for sed:
string s="sed -i s/hey/ho/g file0102.txt";
system(s.c_str());
Related
This question already has answers here:
Deleting specific line from file
(3 answers)
Closed 4 years ago.
I want to search for a string in a text file and delete the whole line when it's found. I want to write this in C++.
I've tried solutions in C#, and I've tried creating temporary files. Nothing works for me.
Here's my code so far:
void MainForm::WriteToTextFile(){
ifstream stream("text.txt");
string line;
bool found = false;
while (std::getline(stream, line) && !found)
{
if (line.find("Delete_This_Line") != string::npos){ // WILL SEARCH "Delete_This_Line" in file
found = true;
line.replace(line.begin(), line.end(), "\n");
stream.close();
}
I expected that the text file would be modified but nothing has changed.
You don't write anything to the file.
And for text files, you can't simply "replace" text, not unless the replacement is the exact same length as the old text you want replaced.
One common way to solve your problem is to read from the original file, writing to a temporary file. When you find the text you want to be replaced then you write the new text to the temporary file. Once you're done then you close both files, and rename the temporary file as the original file, replacing it with your new modified content.
You modify only a string in the memory, how can you expect that change the content of the read file ?
Note also to continue to try to read into the file while you closed it, you test found too late after the getline(), and is more simple to just add a break
std::getline duplicates the line to another string object inside memory. Modifying that string will not change the contents of the file.
A possible solution is to recreate the file using input and output file streams and avoid copying just the desired line. Here is an untested example:
#include <fstream>
#include <cstdio>
#include <string>
#include <iostream>
using namespace std;
bool replace_line(string filename, string key, string new_content)
{
{
ifstream stream(filename);
ofstream ofs(filename + ".out");
string line;
bool found = false;
while (std::getline(stream, line))
{
if (line.find(key) != string::npos){
found = true;
ofs << new_content;
} else {
ofs << line;
}
}
}
remove(file);
rename(file + ".out", filename);
return found;
}
I am trying to read about 2 lines from a file of text into a std::string in c plus plus. I have looked through several answers and found none that work on my device. Can anyone tell me what I am doing wrong? The method is currently returning a null string, and doesn't correctly open the file or read it at all.
std::string readFile(std::string filename) {
std::ifstream infile;
infile.open(filename);
std::string output;
if (infile.is_open()) {
while(infile.good()) {
infile >> output;
}
}
infile.close();
return output;
}
Not sure what file you are trying to open but that's a completely separate problem. The code you've written will open a file if you give it a path to a file that it can open. Check your current working directory and confirm the path is correct.
Even after you solve that problem, you're going to have more problems though.
I expect that you are confused because you are repeatedly overwriting output with this line:
infile >> output;
perhaps you meant to declare output as a std::stringstream
And for me it doesn't return an empty string, it returns the last word of the file. I guess it depends what's in your file.
I just wondering cause i have a text file containing STATUS:USERID:PASSWORD in accounts.txt
example it would look like this:
OPEN:bob:askmehere:
OPEN:john:askmethere:
LOCK:rob:robmypurse:
i have a user input in my main as such user can login 3x else status will change from OPEN to LOCK
example after 3 tries of john
before:
OPEN:bob:askmehere:
OPEN:john:askmethere:
LOCK:rob:robmypurse:
after:
OPEN:bob:askmehere:
LOCK:john:askmethere:
LOCK:rob:robmypurse:
what i have done is:
void lockUser(Accounts& in){
// Accounts class consist 3 attributes (string userid, string pass, status)
ofstream oFile;
fstream iFile;
string openFile="accounts.txt";
string status, userid, garbage;
Accounts toupdate;
oFile.open(openFile);
iFile.open(openFile);
while(!iFile.eof()){
getline(iFile, status, ':');
getline(iFile, userid, ':');
getline(iFile, garbage, '\n');
if(userid == in.getUserId()){
toupdate.setUserId(in.getuserId());
toupdate.setPassword(in.getPassword());
toupdate.setStatus("LOCK");
break;
}
//here i should update the account.txt how do i do that?
ofile.open(openFile);
ofile<<toupdate.getStatus()<<":"<<toupdate.getUserId()":"<<toupdate.getPassword()<<":"<<endl;
}
There are two common ways to replace or otherwise modify a file. The first and the "classic" way is to read the file, line by line, check for the line(s) that needs to be modified, and write to a temporary file. When you reach the end of the input file you close it, and rename the temporary file as the input file.
The other common way is when the file is relatively small, or you have a lot of memory, is to read it all into memory, do the modification needed, and then write out the contents of the memory to the file. How to store it in memory can be different, like a vector containing lines from the file, or a vector (or other buffer) containing all characters from the file without separation.
Your implementation is flawed because you open the output file (which is the same as the input file) inside the loop. The first problem with this is that the operating system may not allow you to open a file for writing if you already have it open for reading, and as you don't check for failure from opening the files you will not know about this. Another problem is if the operating system allows it, then your call to open will truncate the existing file, causing you to loose all but the very first line.
Simple pseudo-ish code to explain
std::ifstream input_file("your_file");
std::vector<std::string> lines;
std::string input;
while (std::getline(input_file, input))
lines.push_back(input);
for (auto& line : lines)
{
if (line_needs_to_be_modified(line))
modify_line_as_needed(line);
}
input_file.close();
std::ofstream output_file("your_file");
for (auto const& line : lines)
output_file << line << '\n';
Use ReadLine and find the line you wanna replace, and use replace to replace the thing you wanna replace. For example write:
string Example = "Text to find";
openFile="C:\\accounts.txt"; // the path of the file
ReadFile(openFile, Example);
OR
#include <fstream>
#include <iostream>
#include <string>
int main() {
ifstream openFile;
string ExampleText = BOB;
openFile("accounts.txt");
openFile >> ExampleText;
openFile.replace(Example, "Hello");
}
I want to read and write compressed file with my C++ script. For this purpose, I use the gzstream lib. It works fine with a very simple example like this :
string inFile="/path/inputfile.gz";
igzstream inputfile;
ogzstream outputfile("/path/outputfile.gz");
inputfile.open(inFile.c_str());
// Writing from input file to output file
string line;
while(getline(inputfile, line)) {
outputfile << line << endl;
}
But in my C++ script, things are more complicated and my output files are created within a dynamic vector.
For UNcompressed files, this way worked very fine :
string inFile="/path/uncompressedInputFile.ext";
ifstream inputfile;
vector <ofstream *> outfiles(1);
string outputfile="/path/uncompressedOutputFile.ext";
outfiles[1] = new ofstream(outputfile.c_str());
inputfile.open(inFile.c_str());
string line;
while(getline(inputfile, line)) {
*outfiles[1] << line << endl;
}
Now with compressed file, this way produces me corrupted files :
string inFile="/path/compressedFile.gz";
igzstream inputfile;
vector <ogzstream *> outfiles(1);
string outputfile="/path/compressedOutputFile.gz";
outfiles[1] = new ogzstream(outputfile.c_str());
inputfile.open(inFile.c_str());
string line;
while(getline(inputfile, line)) {
*outfiles[1] << line << endl;
}
I got a "compressedOutputFile.gz" in my path, not empty, but when trying to uncompressed it I got "unexpected end of file" which, I guess, means the file is corrupted....
What's wrong with it ? Can anyone please help me ?! :)
In the simple example, the GZip file is closed automatically when the ofstream is destroyed, which flushes its remaining buffer to disk.
In the dynamic example, you're not closing because the object is being created on the heap. In both cases, this could result in the loss of data at the end of the file, depending on the format. Since GZip is compressed, it's more likely to lose more relevant data, resulting in a more obvious failure.
The best solution is to create a vector<unique_ptr<ogzstream> >, which cause it to automatically destroy streams when they go out of scope. The less optimal solution is to remember to manually delete each pointer prior to exiting the function.
Edit: And as a quick note, as pointed out by #doctorlove in the original comments, you need to use the correct index, otherwise you're causing other issues.
I managed to successfully read the text in a file but it only reads until it hits an empty space, for example the text: "Hi, this is a test", cout's as: "Hi,".
Removing the "," made no difference.
I think I need to add something similar to "inFil.ignore(1000,'\n');" to the following bit of code:
inFil>>text;
inFil.ignore(1000,'\n');
cout<<"The file cointains the following: "<<text<<endl;
I would prefer not to change to getline(inFil, variabel); because that would force me to redo a program that is essentially working.
Thank you for any help, this seems like a very small and easily fixed problem but I cant seem to find a solution.
std::ifstream file("file.txt");
if(!file) throw std::exception("Could not open file.txt for reading!");
std::string line;
//read until the first \n is found, essentially reading line by line unti file ends
while(std::getline(file, line))
{
//do something line by line
std::cout << "Line : " << line << "\n";
}
This will help you read the file. I don't know what you are trying to achieve since your code is not complete but the above code is commonly used to read files in c++.
You've been using formatted extraction to extract a single string, once: this means a single word.
If you want a string containing the entire file contents:
std::fstream fs("/path/to/file");
std::string all_of_the_file(
(std::istreambuf_iterator<char>(filestream)),
std::istreambuf_iterator<char>()
);