loop variable inside the loop question

[Gyiove]

Hello everyone,

for(int i = 0) {
    for( int j = 0 ) { } }

int i, j;
for(i = 0) {
    for( j = 0 ) { } }

1. Should I be worried about declaring a variable inside the loop like this or would the compiler 'optimize' it for me anyways?
( running c++ compiles with default settings )

2. What about other variables declared inside the loop?
Thanks!

[PacR]

I think you should not be worried.

if you are using for loop then is best to do like this:

for (int i = 0; i < TimesToLoop; i++){

}

Also dont declare variables inside loop like this:

while(){
int i=0; NOT GOOD!
}

[Vabi]

you can declare the variable inside for loop that is good habit

[helios]

Basic types can be allocated on the stack in zero time, so these two snippets have identical performance:

int i;
/*some loop*/{
    i = 0;
    // etc.
}

/*some loop*/{
    int i = 0;
    // etc.
}

Likewise for these:

for (int i = 0; i < n; i++){
    for (int j = 0; j < m; j++){
        // etc.
    }
}

int i, j;
for (i = 0; i < n; i++){
    for (j = 0; j < m; j++){
        // etc.
    }
}

In the general case, the same does not hold true for objects. A class may define arbitrarily complex constructors. For example, a constructor might open a TCP connection and get some info from a web server, which may take an unknown amount of time. You need to decide on a case-by-case basis when and where to allocate an object, taking into account the things its constructor and destructor do.