第五章 指针与数组

5.2 指针与函数参数

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
 
int getch(void);
void ungetch(int);
 
/*getint 函数：将输入中的下一个整型数赋值给*pn */
int getint(int* pn)
{
    int c, sign;
 
    while (isspace(c = getch())) /*跳过空白符*/
        ;
    if (!isdigit(c) && c != EOF && c != '+' && c != '-') {
        ungetch(c); /*输入不是一个数字 */
        return 0;
    }
    sign = (c == '-') ? -1 : 1;
    if (c == '+' || c == '-')
        c = getch();
    for (*pn = 0; isdigit(c); c = getch())
        * pn = 10 * *pn + (c - '0');
    *pn *= sign;
    if (c != EOF)
        ungetch(c);
    return c;
}
 
#define BUFSIZE 100
 
char buf[BUFSIZE];
int bufp = 0;
 
int getch(void)
{
    return (bufp > 0) ? buf[--bufp] : getchar();
}
 
void ungetch(int c)
{
    if (bufp >= BUFSIZE)
        printf("ungetch: too many characters
");
    else
        buf[bufp++] = c;
}
 
int main()
{
    int n, array[10];
    for (n = 0; n < 10 && getint(&array[n]) != EOF; n++)
        ;
    for (n = 0; n < 10; n++)
        printf("%d
", array[n]);
    return 0;
}

5.6 指针数组以及指向指针的指针

#include <stdio.h>  
#include <string.h>  
#include <stdio.h>
#define MAXLINES 5000 /*最多可以输入5000行*/  
#define MAXLEN 1000 /*max length of any input line*/  
#define ALLOCSIZE 10000 /*size of available space */  

char *lineptr[MAXLINES]; /*指向所有行的指针*/  
static char allocbuf[ALLOCSIZE]; /*storage for alloc*/  
static char *allocp = allocbuf; /*next free position */       

int readlines(char *lineptr[], int nlines);  
void writelines(char *lineptr[], int nlines);  
int add_getline(char *, int);  
char *alloc(int);  
void qsort(char *lineptr[], int left, int right);  

/* sort input lines*/  
int main()
{  
    int nlines; /*number of input lines read*/  

    if ((nlines = readlines(lineptr, MAXLINES)) > 0) {  
        qsort(lineptr, 0, nlines - 1);  
        writelines(lineptr, nlines);  
        return 0;  
    }  
    else{  
        printf(" error : input too big to sort 
");  
        return 1;  
    }     
}    

/*readlines : read input lines*/  
int readlines(char *lineptr[], int maxlines)
{  
    int len, nlines;  
    char *p, line[MAXLEN];  

    nlines = 0;  
    printf("please input the strings need to sort
");
    while ((len = add_getline(line, MAXLEN)) > 0) {  
        if (nlines >= maxlines || (p = alloc(len)) == NULL) {  
        return -1;  
        }  
        else{  
        line[len - 1] = '';/*删除换行符*/  
        strcpy(p, line);  
        lineptr[nlines++] = p;  
        }  
    }  
    return nlines;  
}  

/*writelines : write output lines */  
void writelines(char *lineptr[], int nlines)
{  
    int i ;  
    printf("
");
    printf("output the sorted strings is:
");
    for ( i = 0; i < nlines; i ++) {  
        printf("%s
", lineptr[i]);  
    }  
}  

/************************************************************************/  
/* qsort : sort v[left]...v[right] into increasing order 
************************************************************************/  
void qsort(char *v[], int left, int right)
{  
    int i , last;  
    void swap(char *v[], int i , int j);//声明交换函数  

    if (left >= right) {  
        return;  
    }  

    swap(v, left, (left + right) / 2);  
    last = left;  
    for (i = left + 1; i <= right; i ++) {  
        if (strcmp(v[i], v[left]) < 0) {  
        swap(v, ++last, i);  
        }  
    }  
    swap(v, left, last);  
    qsort(v,left, last - 1);  
    qsort(v, last + 1, right);  
}  

void swap(char *v[], int i , int j)
{  
    char *temp;  

    temp = v[i];  
    v[i] = v[j];  
    v[j] = temp;  
}  

/************************************************************************/  
/* getline : get line into s, return length 
************************************************************************/  
int add_getline(char s[], int lim)
{  
    int c, i;  

    i = 0;  
    while ( --lim > 0 && (c = getchar()) != EOF && c != '
') {  
        s[i++] = c;  
    }  

    if (c == '
') {  
        s[i++] = c;  
    }  
    s[i] = '';  
    return i;  
}  

char *alloc(int n)
{/* return pointer to n characters*/  
    if (allocbuf + ALLOCSIZE - allocp >= n) {  
        allocp += n;  
        return allocp - n;/*old p*/  
    }  
    else{ /* not enough room*/  
        return 0;  
    }  
}  
编译执行，显示：
please input the strings need to sort
paul 
ray
allen
kobe
abi
bill

output the sorted strings is:
abi
allen
bill
kobe
paul
ray