Aprenda GCC | Compiler Directives and Advanced Control

#pragma GCC diagnostic [action] [warning-name]

#pragma: Directive for the compiler
GCC diagnostic: Indicates a diagnostic command specific to GCC
action: What to do: ignored, warning, or error
warning-name: The name of the warning, e.g. -Wunused-variable, -Wreturn-type, etc.

The function broken_function has a return type of int, but it does not contain a return statement.
This means the function doesn't return a value, even though its declared return type requires one — which violates the function's contract.

main.c


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#include <stdio.h>

int broken_function() {
    // warning: no return statement in function returning non-void [-Wreturn-type]
}

int main() {
    int result = broken_function();
    printf("Result: %d\n", result);
    return 0;
}

The directive #pragma GCC diagnostic error "-Wreturn-type" changes the compiler's behavior so that a warning about a missing return statement in a function with return type int is treated as a compilation error instead of just a warning.

main.c


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#include <stdio.h>

#pragma GCC diagnostic push
#pragma GCC diagnostic error "-Wreturn-type"
int broken_function() {
    //  error: no return statement in function returning non-void [-Werror=return-type]
}
#pragma GCC diagnostic pop

int main() {
    int result = broken_function();
    printf("Result: %d\n", result);
    return 0;
}

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Seção 4. Capítulo 3

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#pragma GCC diagnostic [action] [warning-name]

#pragma: Directive for the compiler
GCC diagnostic: Indicates a diagnostic command specific to GCC
action: What to do: ignored, warning, or error
warning-name: The name of the warning, e.g. -Wunused-variable, -Wreturn-type, etc.

main.c


              1234567891011
            
#include <stdio.h>

int broken_function() {
    // warning: no return statement in function returning non-void [-Wreturn-type]
}

int main() {
    int result = broken_function();
    printf("Result: %d\n", result);
    return 0;
}

main.c


              1234567891011121314
            
#include <stdio.h>

#pragma GCC diagnostic push
#pragma GCC diagnostic error "-Wreturn-type"
int broken_function() {
    //  error: no return statement in function returning non-void [-Werror=return-type]
}
#pragma GCC diagnostic pop

int main() {
    int result = broken_function();
    printf("Result: %d\n", result);
    return 0;
}

Tudo estava claro?

Obrigado pelo seu feedback!

Seção 4. Capítulo 3