I'm handling a file using fstream, and I need to read and write to it. However, even using std::ios:in, the file continues to be created if it does not exist:
std::fstream file("myfile.txt", std::ios::in | std::ios::out | std::ios::app);
Any thoughts?
Thanks in advance!
Read documentation carefully:
std::basic_filebuf<CharT,Traits>::open - cppreference.com
The file is opened as if by calling std::fopen with the second argument (
mode) determined as follows:
mode openmode & ~ate Action if file already exists Action if file does not exist "r" in Read from start Failure to open "w" out, out|trunc Destroy contents Create new "a" app, out|app Append to file Create new "r+" out|in Read from start Error "w+" out|in|trunc Destroy contents Create new "a+" out|in|app, in|app Write to end Create new "rb" binary|in Read from start Failure to open "wb" binary|out, binary|out|trunc Destroy contents Create new "ab" binary|app, binary|out|app Write to end Create new "r+b" binary|out|in Read from start Error "w+b" binary|out|in|trunc Destroy contents Create new "a+b" binary|out|in|app, binary|in|app Write to end Create new
This should explain everything.
Just drop app flag and you done.
There are different approaches, you can do it the old way
std::fstream file("myfile.txt", std::ios::in | std::ios::out); // edited after comment
if (!file)
{
// Can't open file for some reason
}
Or you can use standard library std::filesystem::exists introduced in C++17. Read more about it.
if (std::filesystem::exists("myfile.txt")) { // Exists }
Remember that file can exist but you can fail to interact with it (read/write from/to it).
If needed:
g++ -std=c++17 yourFile.cpp -o output_executable_name
if (std::filesystem::exists("myfile.txt")) ...appfixes issue vote to close as typo.