Making types the same..

[kermit]

I am playing around with C++ again, and I have the following line which is causing a warning from g++:

vector<string> v;
...
for(int i = 0; i < v.size(); i++) {

The warning is:

vec.cpp: In function ‘int main()’:
vec.cpp:16: warning: comparison between signed and unsigned integer expressions

What do I do to satisfy the compiler? I assume I would declare i in some way connected v?

[laserlight]

What do I do to satisfy the compiler? I assume I would declare i in some way connected v?

Write:

for(vector<string>::size_type i = 0; i < v.size(); i++) {

[kermit]

Perfect, thanks. I am assuming that as the text I am using progresses, it will cover this sort of thing.

[anon]

Unlikely, if it hasn't done it so far...

Even using a simple unsigned might be enough to silence the computer and be more correct (although perhaps it can fail if sizeof(std::vector<T>::size_type) > sizeof(unsigned) and v.size() > std::numeric_limits<unsigned>::max() )

Iterators would be another good choice for iterating over a container, and if possible std::for_each might be even better (or BOOST_FOREACH and similar).

[kermit]

Unlikely, if it hasn't done it so far...

Perhaps I will switch texts then. The one I am currently using is Eckel's Thinking in C++. I am in possession of another one (C++ Primer) that I have heard good things about.

[laserlight]

Perhaps I will switch texts then. The one I am currently using is Eckel's Thinking in C++. I am in possession of another one (C++ Primer) that I have heard good things about.

I would recommend Accelerated C++ given that you already have some background.

[kermit]

Thanks, I will check it out.

[anon]

Thinking in C++ actually seems quite OK. He actually seems to use size_t generally for such loops (if I'm not mistaken Container::size_type is a typedef of Allocator::size_type which in turn is supposed to be the typedef for std::size_t.

--The typedef members pointer, const_pointer, size_type, and differ-
ence_type are required to be T*, T const*, size_t, and ptrdiff_t,
respectively.

[CornedBee]

That's only guaranteed for the default allocator. But I've never heard of an allocator that does it differently.

[bboozzoo]

being extra lazy you can always use std::for_each from <algorithm> or if you need to break the loop explicitly at some point (and writing C++ code, you're likely to have Boost laying around) BOOST_FOREACH might work