Comparing strings lexicographically

Question

I thought that if I used operators such as ">" and "<" in c++ to compare strings, these would compare them lexicographically, the problem is that this only works sometimes in my computer. For example

if("aa" > "bz") cout<<"Yes"; 

This will print nothing, and thats what I need, but If I type

if("aa" > "bzaa") cout<<"Yes"; 

This will print "Yes", why is this happening? Or is there some other way I should use to compare strings lexicographically?

Answer 1

Comparing std::string -s like that will work. However you are comparing string literals. To do the comparison you want either initialize a std::string with them or use strcmp:

if(std::string("aa") > std::string("bz")) cout<<"Yes"; 

This is the c++ style solution to that.

Or alternatively:

if(strcmp("aa", "bz") > 0) cout<<"Yes"; 

EDIT(thanks to Konrad Rudolph's comment): in fact in the first version only one of the operands should be converted explicitly so:

if(std::string("aa") > "bz") cout<<"Yes"; 

Will again work as expected.

EDIT(thanks to churill's comment): since c++14 you can use string literals:

if("aa"s > "bz") cout<<"Yes"; 

Answer 2

You are comparing "primitive" strings, which are of type char const *.

The following is essentially equivalent to your example:

char const * s1 = "aa"; char const * s2 = "bz"; if ( s1 > s2 ) cout<<"Yes"; 

This is comparing the pointers (the memory addresses of the strings), not the contents.

@izomorphius has suggested some good solutions.