/in/foo.cc: In function 'int main()':
/in/foo.cc:11:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if (si >= s.size()) {
         ~~~^~~~~~~~~~~
/in/foo.cc:15:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if (si + len > s.size()) {
         ~~~~~~~~~^~~~~~~~~~