Why use strcmp instead of == in C++?

c++ strcmp
Fawad Nasim picture Fawad Nasim · Mar 22, 2014 · Viewed 7.7k times · Source

I wonder my code works perfectly fine either using strcmp or simply == in C++ for comparing 2 char arrays. Can any one justify the reason of using strcmp instead of ==;

Answer

WiSaGaN picture WiSaGaN · Mar 22, 2014

strcmp compares the actual C-string content, while using == between two C-string is asking if these two char pointers point to the same position.

If we have some C-string defined as following:

char string_a[] = "foo";
char string_b[] = "foo";
char * string_c = string_a;

strcmp(string_a, string_b) == 0 would return true, while string_a == string_b would return false. Only when "comparing" string_a and string_c using == would return true.

If you want to compare the actual contents of two C-string but not whether they are just alias of each other, use strcmp.

For a side note: if you are using C++ instead of C as your question tag shows, then you should use std::string. For example,

std::string string_d = "bar";
std::string string_e = "bar";

then string_d == string_e would return true. string_d.compare(string_e) would return 0, which is the C++ version of strcmp.

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