cb21a_c++_string对象的比较

*cb21a_c++_string对象的比较
s.compare(s2)--区分大小的
s.compare(pos1,n1,s2)
s.compare(pos1,n1,s2,pos2,n2)
s.compare(cp)
s.compare(pos1,n1,cp)
s.compare(pos1,n1,cp,n2)

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