c++ - Is ofstream thread safe?

Question

I am working on a program, which uses multiple std::ifstreams for reading a binary file, one std::ifstream for each thread. Now I need to know, if std::ofstream is thread-safe on Windows and Linux for writing in a same file. I am using using only one std::ofstream and using for multiple threads.
I am reading different blocks using using each thread and writing those block in output file using seekp() and write(). Currently it is working for me but whether it is problematic for big files.

Is std::ofstream thread safe?

Answer 1

If I haven't misunderstood you - no, nothing in the standard library is thread safe (except the std::thread specific things, of course (from C++11 and later)). You need additional synchronization.

Even more - if there are several processes, reading from/writing to these files, you need to lock the files, to sync the access.