Stringstream c++ while loop

Question

Program finds integeres between commas like "2,33,5" -> 2 33 5. The problem is why is it working if I put for example string like "0,12,4". shouldn't the stringstream put 0 into tmp so the loop was like while(0) at the beginning?

 vector<int> parseInts(string str) {
 stringstream ss(str);   //getting string 
 vector<int> result;
 char ch;
 int tmp;
 while(ss >> tmp) {      //while(IS IT INTEGER ALREADY OR NOT?)
     result.push_back(tmp);
     ss >> ch;           
}
return result;

@JakeFreeman Look more closely at the example input. There is no whitespace. — Code-Apprentice, Dec 18 '17 at 22:01
`>>The problem is why is it working if I put for example string like "0,12,4"` why is it a problem? You don't want it to read 0? — Killzone Kid, Dec 18 '17 at 22:04
@KillzoneKid He's just surprised that it works, he thought `while()` would be testing the value of being extracted. — Barmar, Dec 18 '17 at 22:06

Code-Apprentice · Accepted Answer · 2017-12-18T22:41:23.507

shouldn't the stringstream put 0 into tmp so the loop was like while(0) at the beginning?

The while condition is ss >> tmp. If you look at the documentation for cin, you will find that operator>>() returns a istream&. It does not return the input that you just read, in this case the int value 0.

In addition, istream (or one of it's base classes) overloads operator bool() which allows istream objects to be implicitly converted to a bool, the type required as the result of a while statements condition. An istream object will evaluate as false whenever an error occurs during the call to operator>>(). If there is no error, then it evaluates to true.

Since the input 0 is a valid int, the while loop continues the next iteration.

Thank u mister, u dispelled my all doubts. – NGC 6543 Dec 18 '17 at 22:33 — NGC 6543, Dec 18 '17 at 22:33

Stringstream c++ while loop

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