6.3 How Not to Use std::strcmp

The function std::strcmp compares two C-style strings and returns zero if they are equal and nonzero if they are different. To check whether two C-style strings are equal, we use code like the following:

    // Check for equal
    if (std::strcmp(string1, string2) == 0) 
       std::cout << "Strings equal\n"; 
    else 
       std::cout << "Strings not equal\n"; 

Some programmers omit the comment and the == 0 clause, leading to the following, confusing code:

    if (std::strcmp(string1, string2)) 
        std::cout << "......"; 

At first glance, this program obviously compares two strings and executes the std::cout statement if they are equal. Unfortunately, the obvious is wrong. If the strings are equal, std::strcmp returns zero, and the std::cout is not executed. Because of this backwards behavior, you should be very careful in your use of strcmp and always comment its use.

(The problem with std::strcmp is another reason that C++ style strings are easier to use than the old C-style strings.)