Here's an (admittedly brain-dead) refactoring algorithm I've performed on several occasions:

1. Start with a .cpp file that compiles cleanly and (AFAICT) works correctly.
2. Read through the file, and wherever there is a local/stack-variable declared without the const keyword, prepend the const keyword to its declaration.
3. Compile the .cpp file again
4. If any fresh compile-time errors are reported, examine the relevant lines of code to determine why -- if it turns out the local-variable legitimately does need to be non-const, remove the const keyword from it; otherwise fix whatever underlying issue the const keyword's addition has revealed.
5. Goto (3) until the .cpp file again compiles cleanly

Setting aside for the moment whether or not it's a good idea to "const all the local variables", is there any risk of this practice introducing a run-time/logic error into the program that wouldn't be caught at compile-time? AFAICT this seems "safe" in that it won't introduce regressions, only compile-time errors which I can then fix right away; but C is a many-splendored thing so perhaps there is some risk I haven't thought of.

CodePudding user response：

const has no runtime implications, that the compiler will not tell you at compile time and fail the build.

CodePudding user response：

If you're willing to accept a contrived example, you could enter the world of undefined behavior.

void increment(int & num)
{
      num;
}

int main()
{
    int n = 99;
    increment(const_cast<int&>(n));
    cout << n;
}

The above compiles and outputs 100. The below compiles and is allowed to do whatever it wants (but happened to output 99 for me). Modifying a const object through a non-const access path results in undefined behavior.

void increment(int & num)
{
      num;
}

int main()
{
    const int n = 99;
    increment(const_cast<int&>(n));
    cout << n;
}

Yes, this is contrived because why would someone do a const_cast on a non-const object? On the other hand, this is a simple example. Maybe in more complex code this might actually come up. Shrug I won't claim that this is a big risk, but it does fall under "any risk", as stated in the question.