I need some help on deleting the last character in a txt file. For example, if my txt file contains 1234567, I need the C++ code to delete the last character so that the file becomes 123456. Thanks guys.
The only way to do this in portable code is to read in the data, and write out all but the last character.
If you don't mind non-portable code, most systems provide ways to truncate a file. The traditional Unix method is to seek to the place you want the file to end, and then do a write of 0 bytes to the file at that point. On Windows, you can use SetEndOfFile. Other systems will use different names and/or methods, but nearly all will have the capability in some form.
For a portable solution, something along these lines should do the job:
#include <fstream>
int main(){
std::ifstream fileIn( "file.txt" ); // Open for reading
std::string contents;
fileIn >> contents; // Store contents in a std::string
fileIn.close();
contents.pop_back(); // Remove last character
std::ofstream fileOut( "file.txt", std::ios::trunc ); // Open for writing (while also clearing file)
fileOut << contents; // Output contents with removed character
fileOut.close();
return 0;
}
Here's a more robust method, going off Alex Z's answer:
#include <fstream>
#include <string>
#include <sstream>
int main(){
std::ifstream fileIn( "file.txt" ); // Open for reading
std::stringstream buffer; // Store contents in a std::string
buffer << fileIn.rdbuf();
std::string contents = buffer.str();
fileIn.close();
contents.pop_back(); // Remove last character
std::ofstream fileOut( "file.txt" , std::ios::trunc); // Open for writing (while also clearing file)
fileOut << contents; // Output contents with removed character
fileOut.close();
}
The trick is these lines, which allow you to read the entire file efficiently into the string, and not just a token:
std::stringstream buffer;
buffer << fileIn.rdbuf();
std::string contents = buffer.str();
This is inspired from Jerry Coffin's first solution in this post . It is supposed to be the fastest solution there.
If the input file is not too large, you can do the following:-
1. Read the contents into a character array.
2. Truncate the original file.
3. Write the character array back to the file, except the last character.
If the file is too large, you can possibly use a temporary file instead of a character array. It will be a bit slow though.
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