Question

I made 2 files which are different from the program above one is temp1.h and another is temp2.c to understand how extern is used. So here is temp1.h

#include<stdlib.h>
typedef struct node * bond;
extern int jk;

页: 1

#include<stdio.h>
#include<temp1.h>
struct node {
int data;
};
int main ()
{
bond t1;
t1=(bond)malloc(sizeof(bond));
t1->data=23;
printf("the data is %d
",t1->data);
jk=0;
printf("The variable jk = %d
",jk);
}

and when I compile these as cc -I ./ temp2.c then I get

/tmp/ccdeJCat.o: In function `main :
temp2.c:(.text+0x3c): undefined reference to `jk 
temp2.c:(.text+0x46): undefined reference to `jk 
collect2: ld returned 1 exit status

我在温1.h中宣布了 j,这样我为什么不能在温2.c中开首?

Answer 1

int jk;

上述声明必须在法典中作出某些规定。此外,<代码>jk必须是全球性的。

Answer 2

没有任何与doesn t相联系的物体档案,因此没有定义。

Answer 3

a. 不是 #;temp1.h>

改为“temp1.h”

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