I have run though a code formatting tool to my c++ files. It is supposed to make only formatting changes. Now when I built my code, I see that size of object file for some source files have changed. Since my files are very big and tool has changed almost every line, I dont know whether it has done something disastrous. Now i am worried to check in this code to repo as it might lead to runtime error due to formatting tool. My question is , will the size of object file be changed , if code formatting is changed.?
I would not check your code into the repo without thoroughly checking it first (review, testing).
Pure formatting changes should not change the object file size, unless you've done a debug build (in which case all bets are off). A release build should be not just the same size, but barring your using __DATE__ and such to insert preprocessor content, it should be byte-for-byte the same as well.
If the "reformatting" tool has actually done some micro-optimizations for you (caching repeated access to invariants in local vars, or undoing your having done that unnecessarily), that might affect the optimization choices the compiler makes, which can have an effect on the object file. But I wouldn't assume that that was the case.