Erase a word from a batch file which was added before

Question

    std::ofstream readd(startLoc, ios::out | ios::app);        

    readd << "/Uninstall";

    readd.close();

this is for adding "/Uninstall" in batch file

now i want remove "/Uninstall" from the batch file which i have added using cpp(file handling append concept) in visual studio 2015 IDE

Open the batch file for reading. Read contents into buffer (a `std::string`). Search for sub string `"/Uninstall"`. Remove it from string if found. Write buffer back to batch file (i.e. overwriting it completely). Happy coding. ;-) — Scheff's Cat, Nov 23 '19 at 07:31
what command i should use to remove that text. i am using this: — Yasir Arafat Sharfi, Nov 23 '19 at 08:52
std::fstream readd(startLoc,"r"); readd.erase("/Uninstall"); readd.close(); — Yasir Arafat Sharfi, Nov 23 '19 at 08:53
_what command i should use to remove that text._ How about `std::string::erase()`? — Scheff's Cat, Nov 23 '19 at 08:53
`std::string::erase()` expects indices. You have to make a `std::string::find()` before. — Scheff's Cat, Nov 23 '19 at 08:54
You apply `erase()` to your `std::fstream`. I told you to load contents into a buffer of type `std::string`. — Scheff's Cat, Nov 23 '19 at 08:55
Again: **`std::string::erase()` expects indices.** You have to make a `std::string::find()` before. — Scheff's Cat, Nov 23 '19 at 08:56
but i am using fstream for finding the batch and "r" inside it to read — Yasir Arafat Sharfi, Nov 23 '19 at 08:57
Sorry, do you actually read what I wrote? My first comment: Open the batch file for reading. Read contents into buffer (a `std::string`). Search for sub string `"/Uninstall"`. Remove it from string if found. Write buffer back to batch file (i.e. overwriting it completely). — Scheff's Cat, Nov 23 '19 at 08:58
All these things have been asked and answered a million times in SO and anywhere. Please, try to google. There must be something nearly ready to learn from. Also, there are good online docs.: [cppreference.com](http://www.cppreference.com) and [cplusplus.com](http://www.cplusplus.com). The latter is not that precise but easier to understand for entry-level programmers (IMHO). — Scheff's Cat, Nov 23 '19 at 09:01
sir, can u please write the code as i have written it for append. i'm not getting properly. — Yasir Arafat Sharfi, Nov 23 '19 at 09:06
startLoc is the buffer where i have stored my batch file path — Yasir Arafat Sharfi, Nov 23 '19 at 09:08
To give you a start... This is what I found in a second by [google "c++ read file into string"](https://www.google.com/search?q=c%2B%2B+read+file+into+string): [SO: Read whole ASCII file into C++ std::string](https://stackoverflow.com/a/33635201/7478597). (It was the 1st(!) hit in my google hit list.) — Scheff's Cat, Nov 23 '19 at 09:11
i have read the content inside batch file but while using std::string::find(" /Uninstall") i am getting error again i.e nonstatic member reference must be relative to some object something — Yasir Arafat Sharfi, Nov 23 '19 at 09:29

score 0 · Answer 1 · answered Nov 23 '19 at 09:51

There are of course always many possible solutions, I will explain and show you one of them.

For the sake of some security to prevent data loss, we will NOT immediately work (modifiy) on the original source file. Instead, we will first open a temporary file, then read the source file, replace the searched word and then output the new data to the temporary file.

After all search and replace operations are finished, the original file will be deleted and the temporary file will be renamed to the original one.

For the search and replace functionality, I used in this example the std::regex_replace function. This is very flexible, because you can use regurlar expressions as search and replace strings. But this may be also a little bit difficult for beginners. Anyway, it will of course also replace normal strings as given by the user.

Please note: The proposed implementation does search and replace words, as requested by the OP. Deleting whole lines is not possible at the moment (an empty line will remain).

So, now the program flow.

Get a filename from the OS for the temporary file
Open a new scope, so that all open fstreams will be closed by the destructor automatically
Open the source file and check, if it could be opened. If not, issue error message
Open the temporary file and check, if it could be opened. If not, issue error message
Read the complete source file line by line
Search and replace string in this one line
Store result in temporary file
Delete the original source file
Rename the temporay file to the original

Additionally I added some error handling and status info.

Please see

#include <string>
#include <regex>
#include <vector>
#include <iostream>
#include <fstream>
#include <cstdio>

bool searchAndReplaceWordInFile(const std::string& filename, const std::string& searchString, const std::string& replaceString) {

    // Get a temporary filename
#pragma warning(suppress : 4996)
    const std::string tempFileName = std::tmpnam(nullptr);

    // Result of file operations
    bool result{ true };

    // Open a new scope for the fstreams. The destructor will be called and the files will be closed
    // after the fstreams will fall out of scope
    {
        // Open the source file name
        std::ifstream sourceFile(filename);

        // Check if it could be opened
        if (sourceFile) {

            // Open the temp file
            std::ofstream tempFile(tempFileName);

            // And check, if it could be opened
            if (tempFile) {

                // We will read the text file line by line
                std::string textLine{};

                // Read all lines of text file
                while (std::getline(sourceFile, textLine)) {

                    // Serach, Replace, using regex and output in temp file
                    tempFile << std::regex_replace(textLine, std::regex(searchString), replaceString) << "\n";
                }
            }
            else {
                std::cerr << "*** Error Could not open temp file: " << tempFileName << "\n";
                result = false;
            }
        }
        else {
            std::cerr << "*** Error Could not open source file: " << filename << "\n";
            result = false;
        }
    }
    if (result) {
        // Remove original file and rename temp file to original file
        std::remove(filename.c_str());
        if (std::rename(tempFileName.c_str(), filename.c_str())) result = false;
    }
    return result;
}

int main() {
    if (searchAndReplaceWordInFile("r:\\something.bat", "/Uninstall", ""))
        std::cout << "Success, Done. \n";
    return 0;
}

Erase a word from a batch file which was added before

1 Answers1