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About LinkBacksI don't know why (-1 < s.size()) evaluates to false, when -1 is less than 3.
Code:int main() { string s = "abc"; cout << s.size() << '\n'; if (-1 < s.size()) { cout << "yes"; } else { cout << "no"; } keep_window_open(); }
This is a discussion on Comparing integers within the C++ Programming forums, part of the General Programming Boards category; I don't know why (-1 < s.size()) evaluates to false, when -1 is less than 3. Code: int main() { ...
I don't know why (-1 < s.size()) evaluates to false, when -1 is less than 3.
Code:int main() { string s = "abc"; cout << s.size() << '\n'; if (-1 < s.size()) { cout << "yes"; } else { cout << "no"; } keep_window_open(); }
s.size() returns a string::size_type, which is indirectly a typedef for size_t, which is an unsigned integer type (typically itself a typedef for unsigned int).
So, -1 < s.size() is a comparison between a signed and unsigned integer. The conversion of -1 to an unsigned integer resulted in a number larger than what s.size() returned.
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Is there an easy way to fix this?
Yes, just write:Is there an easy way to fix this?
Code:int main() { string s = "abc"; cout << s.size() << '\n'; cout << "yes"; keep_window_open(); }
C + C++ Compiler: MinGW port of GCC
Version Control System: Bazaar
Look up a C++ Reference and learn How To Ask Questions The Smart Way
laserlight: haha lolo!
really strange, one unsigned other signed and they promote the signed to unsigned?
actually i think you would get a warning, which will ask for a cast, and this will fix the problem, before it annoys you.
Yes, it should indeed prompt a warning. When comparing integers, make sure both are of the same type.
Originally Posted by Adak
For information on how to enable C++11 on your compiler, look here.
よく聞くがいい！私は天才だからね！ ^_^
And at least g++ gives a warning when using -Wall. I'm pretty sure MSVC is the same.
--
Mats
Compilers can produce warnings - make the compiler programmers happy: Use them!
Please don't PM me for help - and no, I don't do help over instant messengers.
So it does, on default warning levels even.
For information on how to enable C++11 on your compiler, look here.
よく聞くがいい！私は天才だからね！ ^_^
Yes, gcc/g++ only needs -W too - I just didn't actually check at which warning level it appears. I normally use -Wall.
--
Mats
Compilers can produce warnings - make the compiler programmers happy: Use them!
Please don't PM me for help - and no, I don't do help over instant messengers.
I'm using Visual C++ and it didn't warn me. I didn't change any warning levels either.
All Visual Studio versions I've used has warned on signed/unsigned comparison, even on default warning levels. What version are you using?
For information on how to enable C++11 on your compiler, look here.
よく聞くがいい！私は天才だからね！ ^_^
Microsoft Visual Studio 2008 Version 9.0.21022.8 RTM
In project settings, under C/C++, make sure "Warning level" is set to 4.
In the output window, check for warnings in the output.
If using the Task List, make sure the Warning button isn't deselected (thus silencing the warnings).
You should get warnings about it.
For information on how to enable C++11 on your compiler, look here.
よく聞くがいい！私は天才だからね！ ^_^
You probably have "warnings" turned down then - check the setting, and set it one or two levels higher (W3 is a good setting, W4 tends to give slightly stupid warnings).
--
Mats
Compilers can produce warnings - make the compiler programmers happy: Use them!
Please don't PM me for help - and no, I don't do help over instant messengers.
But W4 is the only one that can warn about potentially uninitialized variables and unused variables and the use of non-standard extensions, so I suggest leaving it on W4 (level 4).
For information on how to enable C++11 on your compiler, look here.
よく聞くがいい！私は天才だからね！ ^_^
