Error: comparison between signed and unsigned integer expressions [-Wsign-compare]

[Jim]

Hi all, 

When building an or-tools program in C++ on Linux, using the binary distribution, I obtain a lot of signed/unsigned mismatch errors. Here is an example of one:

../or-tools/ubuntu-16.04/include/ortools/util/tuple_set.h: In member function ‘void operations_research::IntTupleSet::InsertAll(const std::vector<std::vector<long long int> >&)’:

../or-tools/ubuntu-16.04/include/ortools/util/tuple_set.h:343:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]

   for (int i = 0; i < tuples.size(); ++i) {

                     ^hier op...

My full error log output is here.

Why are all these mismatches in the code? Does it not matter? I was surprised to see that no question was asked about this yet on this group, so I'm curious what other people think about this.

[Laurent Perron]

Really, it does not matter :-) The code is safe.

And changing i to size_t will create more risk if we use it in some arithmetic operation.

--Laurent

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

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[Jim]

Okay thanks, that is good to know. Then I might need to suppress the errors. Because everytime I build my project 200 of these errors come by.

-Jim

Op donderdag 19 april 2018 11:35:59 UTC+2 schreef Laurent Perron:

[Jim]

Wouldn't it be better to loop using auto though?

Op donderdag 19 april 2018 14:30:00 UTC+2 schreef Jim:

[Laurent Perron]

Nous, it would use size_t in its place, and we are back to the dangerous unsigned arithmetic. 

Writing x -y with unsigned is error prone. 

--Laurent