Re: Useful applications for boolean increments?
Am 02.11.2012 19:31, schrieb Stuart:
I can only imagine one reason why someone would want to use
operator++ on a bool variable, which would be that he wants to
negate the value in a single line:
bool negate (bool value) {
return ++value;
}
Yes, but that doesn't do what you expect, right?
Apparently operator++ does not work like this
Exactly. The specification says that the result of increment on any
bool value is true.
(it seems to invoke operator++ on the internal representation of a
bool):
Not really, the result is specified to be true - that's it. You can
consider it as equivalent to converting 1 (the successor of false) or
2 (the successor of true) back to bool.
The only use case for operator++ on bool I could think of was the
following:
#include <iostream>
#include <vector>
void print(const std::vector<int>& vec) {
bool needComma = false;
for (auto it = vec.begin(); it != vec.end(); ++it) {
if (needComma++)
std::cout << ", ";
std::cout << *it;
}
}
int main () {
std::vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);
print(v);
}
Admittedly, this is a bit far-fetched will probably yield wrong
results for large vectors if bool is implemented using 8bit values.
No, the outcome is independent of representation. It will always be
true after the first incrementation. Otherwise the result of n
incrementations would be dependent on the representation. The
specification requires that the following program would present an
infinite loop:
int main () {
bool v = false;
while (++v) {}
}
Thanks for your feedback,
Daniel Kr?gler
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