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There's a new comparison operator <=> in C++20. However I think in most cases a simple subtraction works well:
int my_strcmp(const char *a, const char *b) { while (*a == *b && *a != 0 && *b != 0) { a++, b++; } // Version 1 return *a - *b; // Version 2 return *a <=> *b; // Version 3 return ((*a > *b) - (*a < *b)); } They have the same effect. I can't really understand the difference.
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Comparison operators — operators that compare values and return true or false . The operators include: > , < , >= , <= , === , and !== . Logical operators — operators that combine multiple boolean expressions or values and provide a single boolean output.
The strict equality operator ( === ) checks whether its two operands are equal, returning a Boolean result. Unlike the equality operator, the strict equality operator always considers operands of different types to be different.
The three-way comparison operator “<=>” is called a spaceship operator. The spaceship operator determines for two objects A and B whether A < B, A = B, or A > B. The spaceship operator or the compiler can auto-generate it for us.
The operator solves the problem with numeric overflow that you get with subtraction: if you subtract a large positive number from a negative that is close to INT_MIN, you get a number that cannot be represented as an int, thus causing undefined behavior.
Although version 3 is free from this problem, it utterly lacks readability: it would take some time to understand by someone who has never seen this trick before. <=> operator fixes the readability problem, too.
This is only one problem addressed by the new operator. Section 2.2.3 of Herb Sutter's Consistent comparison paper talks about the use of <=> with other data types of the language where subtraction may produce inconsistent results.
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