C #error

The #error preprocessor directive indicates error. The compiler gives fatal error if #error directive is found and skips further compilation process.

C #error example

Let's see a simple example to use #error preprocessor directive.

snippet

#include
#ifndef __MATH_H
#error First include then compile
#else
void main(){
    float a;
    a=sqrt(7);
    printf("%f",a);
}
#endif

Output:

Output

Compile Time Error: First include then compile

But, if you include math.h, it does not gives error.

snippet

#include
#include
#ifndef __MATH_H
#error First include then compile
#else
void main(){
    float a;
    a=sqrt(7);
    printf("%f",a);
}
#endif

Output:

Output

2.645751

Related Tutorial

1 C Preprocessor Directives

2 C Macros

3 C #include

4 C #define

5 C #undef

6 C #ifdef

7 C #ifndef

8 C #if

9 C #else

10 C #error

11 C #pragma

Try it

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