Macro definition and program debugging methods in C Language

1. prevent repeated definitions in a header file

The format is as follows:

# Ifndef comdef_h
# Define comdef_h
// Header file content
# Endif

This can be seen at the beginning of many header files, that is, it cannot be understood. What is repeated definition ??? Try a program

• Example 1 test1.c

#include <stdio.h>
int main(int argc,char *argv[])
{
  printf("lsdkfla/n");
}

• Example 2 test2.c

#include <stdio.h>
#include <stdio.h>
int main(int argc,char *argv[])
{
  printf("lsdkfla/n");
}

Editing Using Dynamic files

#gcc test1.c -Wall

The compilation structure is correct ....

#gcc test2.c -Wall 

Oh, no error either ??? What's the purpose of this !!! I don't understand. Is it possible that there will be two stdio. h library connections in the. Out structure compiled by test2.c? I will compile the static library. Compile to a static file:

#gcc -Wall -static test1.c -o test1

Compilation result, no error!

#gcc -Wall -static test2.c -o test2

The compilation structure is correct... Use LS-L to check the file size. Oh, it's as big as it is... What is the function? I thought for a long time... I suddenly thought of writing a header file.

• Example 3 test. h main. c

/*test.h*/ 
#include <stdio.h>
int test(int a)
{
 printf("test .../n");
}

/*main.c*/
#include "test.h"
int main(int argc,char *argv[])
{
    test(4);
}

Compilation Method:

#gcc -Wall main.c

Compilation result, no error .... Continue the test .....

• Example 4 test. h main. c

/* Test. H */

#include <stdio.h>
int test(int a)
{
 printf("test .../n");
}

/*main.c*/
#include "test.h"
#include "test.h"
int main(int argc,char *argv[])
{
    test(4);
}

Compilation result: An error occurred... Haha...

Test. h: 3: Error: 'test' redefinition
Test. h: 3: Error: 'test' is defined here

I finally figured it out ..... So let me add a macro definition .... Example 5 test. h main. c/* test. H */

# Ifndef _ test_h
# DEFINE _ test_h
# Include <stdio. h>
Int test (int)
{
Printf ("test.../N ");
}
# Endif/* end _ test_h */

/*main.c*/
#include "test.h"
#include "test.h"
int main(int argc,char *argv[])
{
    test(4);
}

Compilation Method:

#gcc -Wall main.c

Compilation result: the program is compiled normally without any error message ....

[Edit]

2 prevent the number of bytes of the type produced by different platforms and compilers

Typedef unsigned char Boolean;/* Boolean value type .*/
Typedef unsigned long int uint32;/* unsigned 32 bit value */
Typedef unsigned short uint16;/* unsigned 16 bit value */
Typedef unsigned char uint8;/* unsigned 8 bit value */
Typedef signed long int int32;/* signed 32 bit value */
Typedef signed short int16;/* signed 16 bit value */
Typedef signed Char int8;/* signed 8 bit value */
// The following is not recommended
Typedef unsigned char byte;/* unsigned 8 bit value type .*/
Typedef unsigned short word;/* unsinged 16 bit value type .*/
Typedef unsigned long DWORD;/* unsigned 32 bit value type .*/

[Edit]

3. Get a byte or word on the specified address.

Obtains a word of the specified address.

#define MEM_B(x) (*((byte *)(x)))

Obtains a word of the specified address.

#define MEM_W(x) (*((word *)(x)))

Example 1 test. c

#include <stdio.h>
#define MEM_B(x) (*((byte *)(x)))
int main(int argc,char *argv[])
{
  char a='c';
  printf("&a==%c /n",MEM_B(&a));
}

Compilation Method:

#gcc -Wall test.c

Execution result:

&a==c

[Edit]

4. Calculate the maximum and minimum values.

Definition method:

#define  MAX( x, y ) ( ((x) > (y)) ? (x) : (y) )
#define  MIN( x, y ) ( ((x) < (y)) ? (x) : (y) ) 

Example: test. c

#include <stdio.h>
#define MAX(x,y) (((x)>(y))?(x):(y))
int main(int argc,char *argv[])
{
   printf("max==%d /n",MAX(4,5));
}

Compilation Method:

#gcc -Wall test.c

Execution result:

#max==5

[Edit]

5. Get the offset of a field in the struct.

Definition method:

#define FPOS( type, field ) ( (dword) &((( type *) )0)-> field )

This is the most depressing one, and finally it's done .... Example of depressing typedef and calculation rules: Test. c

#include <stdio.h>
typedef unsigned long dword;
#define FPOS( type,field) (dword)&(((type *)0)->field)
typedef struct test 
{
        int a;
        int b;
        char c ;
}d;
int main(int argc,char *argv[])
{
   printf("offset==%d /n",FPOS(d,b));
}

Compilation Method:

#gcc -Wall test.c

Execution result

#offset==0x4

The "&" operation level is smaller than the "->" operation level.

C language operator table is recommended. </Tr> </table>

[Edit]

6. Obtain the number of bytes occupied by the field in the struct.

Definition method:

#define FSIZ(type,field) sizeof(((type *) 0)->field )

Example: test. c

#include <stdio.h>
#define FSIZ(type,field) sizeof(((type *) 0)->field)
struct test
{
    int a;
    int b;
    char c;
};
int main(int argc,char *argv[])
{
   printf("sizeof==%d /n",FSIZ(struct test,b);
}

Compilation Method:

#gcc -Wall test.c

Execution result:

#sizeof=4

[Edit]

7. convert two bytes into a word in LSB format

Tip: definitions of LSB and MSB

• The LSB (least significant bit) is the "least significant bit ".
• MSB (most significant bit) is "the most significant bit"

Definition Format

#define  FLIPW(ray) ((((word)(ray)[0])* 256)+(ray)[1])

Example: test. c

#include <stdio.h>
typedef unsigned short word;
#define  FLIPW(ray) ((((word)(ray)[0])* 256)+(ray)[1])
int main(int argc,char *argv[])
{
  char test[2]={0x06,0x07};
  printf("LSB==%d /n",FLIPW(test));
}

Compilation Method:

#gcc -Wall test.c

Execution Structure

#1541

??? Which number is ??? 6*256 + 5 = 1541 suddenly came up with an idea. It cannot be changed to a byte order. Let's take a look... Example: test. c

1. Include <stdio. h>

typedef unsigned short word;
#define  FLIPW(ray) ((((word)(ray)[1])* 256)+(ray)[2])
int main(int argc,char *argv[])
{
  char test[2]={0x06,0x07};
  printf("LSB==%d /n",FLIPW(test));
}

Compilation Method:

#gcc -Wall test.c

Execution Structure

#1286

?? Which number is ??? 5*256 + 6 = 1286

[Edit]

8. convert a word into two bytes in LSB format.

Definition method:

#define  FLOPW( ray, val ) (ray)[0] = ((val) / 256); (ray)[1] = ((val) & 0xFF)

[Edit]

9 references

Document 1: macro definition skills in C Language
Http://www.ednchina.com/blog/levension/21415/message.aspx
Document 2:
Http://gawaine.itpub.net/

Document 3:

    http://www.yesky.com/309/1853309.shtml

Operator	Explanation	Combination Method
() []->.	Parentheses (functions, etc.), arrays, two types of structure member access	From left to right
! ~ ++ -- +- * & (Type) sizeof </TD>	Negative, bitwise negative, incremental, decrement, positive and negative, <p> indirect, address fetch, type conversion, and Size Estimation	From right to left
*/%	Multiplication, division, modulo	From left to right
+-	Add, subtract	From left to right
<>	Left shift, right shift	From left to right
<<=>=>	Less than, less than or equal to, greater than or equal to, greater	From left to right
=! =	Equal to, not equal	From left to right
&	Bitwise AND	From left to right
^	Bitwise OR	From left to right
|	By bit or	From left to right
&&	Logic and	From left to right
|	Logic or	From left to right
? :	Condition	From right to left
= + =-= * =/= <P> & = ^ = |=< <=> =	Various assignments	From right to left
,	Comma (Order)	From left to right