What is the #error directive in C++?
The #error directive
#error is a
#error tokens
In the example above, tokens are any sequence of characters separated by spaces. If the compiler encounters an #error directive before compilation, it will halt the compilation and display the tokens as an error in the standard output.
Using the #error directive
The #error directive is normally used to throw an error during conditional compilation.
Take a look:
#include <iostream>using namespace std;int main() {#ifdef PIdouble area = PI * 2 * 2;cout << "Area of a circle of radius 2 is: " << area << endl;#else#error PI is not defined#endifreturn 0;}
In the above example, the PI is not defined error is printed in the standard output because the #ifdef PI evaluates to false, thus, resulting in the execution of the #else clause that contains the #error directive. Here, the #error directive ensures that the compiler will only compile the program if the specified conditions are met; otherwise, the compiler must provide an explanation as to why the program did not compile.
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