c - K&R练习5-3 : passing pointers to functions

Question

#include <stdio.h>
#define MAX 100
void str_cat(char *s, char *t);

int main()
{
    char a[MAX] = "Hello, ";
    char b[MAX] = "world!";
    char *p;
    char *q;
    p = a;
    q = b;
    str_cat(*p, *q);
    printf("The new string is %s.\n", a);

    return 0;
}

void str_cat(char *s, char *t)
{
    while (*s++)
        ;
    while (*s++ = *t++)
        ;
}

编译器错误:

str_cat.c: In function ‘main’:
str_cat.c:13:11: warning: passing argument 1 of ‘str_cat’ makes pointer from integer without a cast [-Wint-conversion]
   str_cat(*p, *q);
           ^
str_cat.c:3:6: note: expected ‘char *’ but argument is of type ‘char’
 void str_cat(char *s, char *t);
      ^~~~~~~
str_cat.c:13:15: warning: passing argument 2 of ‘str_cat’ makes pointer from integer without a cast [-Wint-conversion]
   str_cat(*p, *q);
               ^
str_cat.c:3:6: note: expected ‘char *’ but argument is of type ‘char’

Answer 1

在 str_cat 函数中，您应该传递 str_cat(p,q) 而不是 str_cat(*p, *q)。您的该函数中的代码有问题。在第一个 while 循环中，当 *s = '\0' 时，while 循环将结束。并将 s 递增到下一个地址。因此，在下一个 while 循环中，指针 s 指向的字符串将包含 '\0' 字符。结果将是这样的:“Hello, '\0'world!”。因此，在 str_cat() 调用之后，字符串仍然是“Hello,”。此代码应该按您的预期工作:

#include <stdio.h>
#include <string.h>
#define MAX 100
void str_cat(char *s, char *t);

int main()
{
    char a[MAX] = "Hello, ";
    char b[MAX] = "world!";
    char *p;
    char *q;
    p = a;
    q = b;
    str_cat(p, q);
    printf("The new string is %s.\n", a);

    return 0;
}

void str_cat(char *s, char *t)
{
    while(*s)
        s++;
    while(*s++ = *t++);
}