CODEWITHSUNDEEP
c++ifstream
vad
vad

Reputation: 3

given: ifstream infile("test.txt") is there advantage to use if(!infile)... versus if(infile.good())...?

I came across this code in my reading:

void assure(std::ifstream& infile ) {  
  if(!infile) { /* stuff */}
}

I tested for curiosity using function argument types ifstream& and ifstream, and it seems to work. I was curious how the conditional expression might work. Is this a case of NULL object or empty object? I thought C++ object could not be NULL?

Since !infile works, how is a failed ifstream object represented?

Thanks for the ensuing enlightenment.

Upvotes: 0

Views: 399

Answers (2)

Mats Petersson
Mats Petersson

Reputation: 129314

It won't make any great difference, no. Both will result in very similar code the same behaviour. The difference is in the behaviour on eof, which good will return false for, where operator! sees that as a true. However, this makes little difference in most cases, as the failbit will be set in the fstream state if an attempt to read past the end of file is made - there are some cases when this doesn't happen, but most of the time, it's the same thing.

Upvotes: 0

Karoly Horvath
Karoly Horvath

Reputation: 96258

It uses the negate operator, and it is simply hooked to the fail() check.

It's not entirely the opposite of good(), as that one also checks for EOF (eofbit).

(And yes, a reference always points to an object, the question is meaningless, only a pointer can be NULL).

Upvotes: 2

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