Kursinhalt

C Preprocessing

1. Introduction to Preprocessing

Introduction to Compilation Stages Role of the Preprocessor Preprocessing Commands

2. Macros

Symbolic Constant Macro With Arguments Advanced Usage of Symbolic Constant Cancel Macro Stringify Operators

3. Conditional compilation

Fundamentals of Conditional Compilation Pitfalls and Best Practices

Macro With Arguments

This simple macro calculates the arithmetic mean of two numbers:

main


              12345678
            
#include <stdio.h>
#define MEAN(X,Y) ((X)+(Y))/2

int main() 
{
   printf("Mean: %d\n", MEAN(1053, 6037));
   return 0;
}

To make the macro able to handle non-integer numbers, we change the specifier and change the arguments to non-integer numbers:

main


              123456789
            
#include <stdio.h>
#define MEAN(X,Y) ((X)+(Y))/2

int main() 
{
   double x = MEAN(1057.3, 6038);
   printf("Mean: %0.1f\n", x);
   return 0;
}

This flexibility can be both an advantage and a problem.

main


              12345678
            
#include <stdio.h>
#define SUM(a,b) (a + b)

int main() 
{
   printf("sum: %d\n", SUM(4+5, 2+3));
   return 0;
}

In this case, the compiler perceives the arguments not as integers 9 and 6, but as the expression 4+5+2+3.

An additional pair of parentheses for the arguments when creating a macro does not solve this problem.

For the next task, let's remember what a ternary operator is:

If the expression a > b is true, the program will return a, if the expression is false, the program will return b.

Why not just use functions?

Speed

Macros work at the preprocessor level, meaning they substitute code directly before compilation. This eliminates the overhead associated with calling functions (saving/restoring registers, jumping by address, etc.).

Using macro:

Using function:

Universality of types

Functions require specifying the types of arguments and return values, while macros simply substitute code, so they can work with any type.

main


              123456789
            
#include <stdio.h>
#define MAX(a, b) ((a) > (b) ? (a) : (b))

int main()
{
        int maxInt = MAX(3, 7);           // 7
        float maxFloat = MAX(3.14, 2.71); // 3.14
        return 0;
}

Key takeaways:

Aufgabe

Swipe to start coding

Create a functional macro MAX with two arguments a and b;
Specify a ternary operator for comparing two numbers as the body of the macro;
Display the larger number.

Lösung

Wechseln Sie zum Desktop, um in der realen Welt zu übenFahren Sie dort fort, wo Sie sind, indem Sie eine der folgenden Optionen verwenden

War alles klar?

Danke für Ihr Feedback!

Abschnitt 2. Kapitel 2

Macro With Arguments

This simple macro calculates the arithmetic mean of two numbers:

main


              12345678
            
#include <stdio.h>
#define MEAN(X,Y) ((X)+(Y))/2

int main() 
{
   printf("Mean: %d\n", MEAN(1053, 6037));
   return 0;
}

To make the macro able to handle non-integer numbers, we change the specifier and change the arguments to non-integer numbers:

main


              123456789
            
#include <stdio.h>
#define MEAN(X,Y) ((X)+(Y))/2

int main() 
{
   double x = MEAN(1057.3, 6038);
   printf("Mean: %0.1f\n", x);
   return 0;
}

This flexibility can be both an advantage and a problem.

main


              12345678
            
#include <stdio.h>
#define SUM(a,b) (a + b)

int main() 
{
   printf("sum: %d\n", SUM(4+5, 2+3));
   return 0;
}

In this case, the compiler perceives the arguments not as integers 9 and 6, but as the expression 4+5+2+3.

An additional pair of parentheses for the arguments when creating a macro does not solve this problem.

For the next task, let's remember what a ternary operator is:

If the expression a > b is true, the program will return a, if the expression is false, the program will return b.

Why not just use functions?

Speed

Using macro:

Using function:

Universality of types

Functions require specifying the types of arguments and return values, while macros simply substitute code, so they can work with any type.

main


              123456789
            
#include <stdio.h>
#define MAX(a, b) ((a) > (b) ? (a) : (b))

int main()
{
        int maxInt = MAX(3, 7);           // 7
        float maxFloat = MAX(3.14, 2.71); // 3.14
        return 0;
}

Key takeaways:

Aufgabe

Swipe to start coding

Create a functional macro MAX with two arguments a and b;
Specify a ternary operator for comparing two numbers as the body of the macro;
Display the larger number.

Lösung

Wechseln Sie zum Desktop, um in der realen Welt zu übenFahren Sie dort fort, wo Sie sind, indem Sie eine der folgenden Optionen verwenden

War alles klar?

Danke für Ihr Feedback!

Abschnitt 2. Kapitel 2

Wechseln Sie zum Desktop, um in der realen Welt zu übenFahren Sie dort fort, wo Sie sind, indem Sie eine der folgenden Optionen verwenden