对ctap中p52到p57的例子的思考

2015-05-21

ctap代表C Traps and Pitfalls这本书. 我觉得这本书中p52给出的例子有两个错误:

1. row不该申明为局部变量，而应该申明为全局变量.
2. 在flush函数中的一个for循环里row不应初始化为0.

下面给出这个例子的代码,这个例子打印输出1->42的数字，每页最多输出五行三列.

Code

    #include <stdio.h>

    #define NROWS   5
    #define NCOLS   3
    #define BUFSIZE (NROWS * (NCOLS - 1))

    static int buffer[BUFSIZE];
    static int row = 0;
    int *bufptr = buffer;

    void print(int n);
    void printnum(int num);
    void printnl();
    void printpage();
    void flush();

    int main()
    {
        int i;
        for(i = 0; i < 42; i++)
            print(i);
        flush();

        return 0;
    }

    void print(int n){
        if(bufptr == &buffer[BUFSIZE}) {
            int *p;
            for(p = buffer + row; p < bufptr; p += NROWS)
                printnum(*p);
            printnum(n);
            printnl();
            if(++row == NROWS) {
                row = 0;
                bufptr = buffer;
                printpage();
            }
        }else {
            *bufptr++ = n;
        }
    }

    void printnum(int num) {
        printf("%d\t", n);
    }

    void printnl() {
        printf("\n");
    }

    void printpage() {
        printf("------------------");
        printnl();
    }

    void flush() {
        int k = bufptr - buffer;
        if (k > NROWS)
            k = NROWS;
        if (k > 0) {
            for (; row < k; row++) {
                int *p;
                for (p = buffer + row; p < bufptr; p += NROWS)
                    printnum(*p);
                printnl();
            }
            printpage();
        }
    }

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