2010年12月2日 星期四

function point (附上sample code)

首先感謝checko無私分享

1. 設定function point, 沒有回傳值, 沒有輸入參數


#include

void (*pFun) (); //create a function point and return void

void funA ()
{
        printf("A\n");  //if you set pFun = funA, and call pFun, it will show "A"
}

void funB ()
{
        printf("B\n"); //if you set pFun = funB and call pFun, it will show "B"
}

int main(int argc, char *argv[])
{
        pFun = funA;  //set pFun = funA
        pFun();

        pFun = funB;  //set pFun = funB
        pFun();
}

輸出

nelsonchung@gps1004:~/test/funpoint$ vim funpoint1.c
nelsonchung@gps1004:~/test/funpoint$ gcc funpoint1.c -o a.out
nelsonchung@gps1004:~/test/funpoint$ ./a.out
A
B

2. 設定function point, 沒有回傳值, 有輸入參數

#include

void (*pFun) (int i); //create a function point and have one arg

void funA (int i)  //if you set pFun = funA, and set arg, it will show the number the same with you input
{
        printf("A = %d\n",i);
}

void funB (int i)
{
        printf("B = %d\n",i);
}

int main(int argc, char *argv[])
{
        pFun = funA;
        pFun(1);

        pFun = funB;
        pFun(2);
}

輸出
nelsonchung@gps1004:~/test/funpoint$ vim funpoint2.c
nelsonchung@gps1004:~/test/funpoint$ gcc funpoint2.c -o b.out
nelsonchung@gps1004:~/test/funpoint$ ./b.out
A = 1
B = 2

3. 設定function point, 有回傳值, 有輸入參數

#include

int (*pFun) (int i); //create a function point, have one arg input and have return value

int funA (int i)
{
        printf("funA: input %d\n",i);
        return i;
}

int funB (int i)
{
        printf("funB: input %d\n",i);
        return i;
}

int main(int argc, char *argv[])
{
        pFun = funA;
        printf("call pFun = %d\n", pFun(1));


        pFun = funB;
        printf("call pFun = %d\n", pFun(2));
}

輸出

nelsonchung@gps1004:~/test/funpoint$ vim funpoint3.c
nelsonchung@gps1004:~/test/funpoint$ gcc funpoint3.c -o c.out
nelsonchung@gps1004:~/test/funpoint$ ./c.out
funA: input 1
call pFun = 1
funB: input 2
call pFun = 2

需求起源

linux kernel code 有許多用struct都用function point先宣告
根據不同的設備
再去指定需要執行的function
ex.
usb 1, 2, 3, 4不同裝置

整個usb架構出來之後

接下來只需要設定相關的function需要做什麼事情
就可以自動呼叫相關的function嚕



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