[英]why am I getting an undefined reference error in C for my implementation of a singly linked list
我收到的错误是这样的
$ gcc -o app llistdriver.c llistlib.c -Wall
llistdriver.c:7: warning: return type defaults to `int'
llistdriver.c: In function `printinsts':
llistdriver.c:15: warning: control reaches end of non-void function
llistlib.c: In function `insert':
llistlib.c:25: warning: statement with no effect
llistlib.c:41: warning: control reaches end of non-void function
/tmp/ccqYmK3M.o:llistdriver.c:(.text+0x157): undefined reference to `_search'
collect2: ld returned 1 exit status
我无法弄清楚为什么我收到此错误消息已写入包含链接列表的方法的库文件。
int search( struct node *front, int val)//
{
while(front != NULL)
{
if( front->modmark == val ) //this is to find the value
return 1; // found it
front=front->next;
}
return 0; // Not found
}
我假设它抱怨主文件中唯一的引用
case 5:
printf("please enter a search value?\n");
scanf("%i",&mark);
choice = search(first,mark);//here
if (choice == -1)
{
printf("the modmark was not found\n");
}
else
{
printf("the first occurence of the mark is at the %i th index of the list",choice);
};
break;
首先,标记是这样定义的变量
struct node *first;
int mark = 0;
我将非常感谢您花了好几个小时尝试调试此错误。 编写C代码是我生命中的祸根。
Ps我检查了所有#include“llistlib.h”,它包含在llistlib.c文件和llistdriver.c文件中。
好吧也许这会让它更清晰
// llistlib.c - 实现listlib.h文件中定义的函数的库#include #include #include“llistlib.h”
void initialise(struct node **ps)
{
printf("initialise function\n");
*ps = NULL; //initialise list to empty
}
int insert(struct node **fn)
{
printf("insert function\n");
struct node *newnode;
newnode = (struct node*) malloc(sizeof (struct node)); //make new node and give it memory
if (newnode == NULL) //if fsiled return to the program saying it failed
return -1;
if (*fn == NULL) // for the first of the list
{
newnode -> next == NULL; // sets the next value to nothing
printf("what mark do you want to enter\n");
scanf("%i",&newnode -> modmark); // this gets the modmark
*fn = newnode; //the head of the list is set to the new node
}
else
{
newnode -> next = *fn; // sets the newnodes next value to the head node
printf("what mark do you want to enter\n");
scanf("%i",&newnode -> modmark); // gets the modmark
*fn = newnode; // the head becomes the new node
printf("%p %i",newnode,newnode->modmark); // just for debugging
}
}
void traverse(struct node *ps)
{
if (ps != NULL) // if the current node is null
{
printf("%p - %i\n",ps,ps -> modmark);
traverse(ps -> next);
}
else
{
printf("your list is empty\n");
}
}
void delete(struct node **dn)
{
printf("delete function\n");
struct node *delnode;
delnode = *dn; //sets the head node so that it can be deleted later
if (delnode != NULL)
{
*dn = delnode -> next; // sets the head to the next node
free(delnode); //deletes the previous head node
}
}
void finish(struct node **ps) //this function goes through the list and removes all items
{
printf("finish function\n");
struct node *finishnode;
finishnode = *ps;
while (finishnode != NULL)
{
*ps = finishnode -> next;
free(finishnode);
finishnode = *ps;
}
int search(struct node *front,int val)
{
while(front != NULL)
{
if( front->modmark == val ) // Assuming struct node has val member which you are trying to compare to
return 1; // found it
front=front->next;
}
return 0; // Not found
}
}
然后是llistdriver.c文件
#include <stdio.h>
#include <stdlib.h>
#include "llistlib.h"
printinsts()
{
printf("Enter:- \n");
printf("\t0 to exit\n");
printf("\t1 to initialise list\n");
printf("\t2 to insert item at front of list\n");
printf("\t3 to delete item from front of list\n");
printf("\t4 to traverse list\n");
printf("\t5 to search through the list\n");
}
int main()
{
int choice;
struct node *first;
int mark = 0;
printinsts();
scanf("%d",&choice);
while (1)
{
switch (choice)
{
case 0 : finish(&first);
exit(0);
break;
case 1 : initialise(&first);
break;
case 2 : if (insert(&first)== -1)
{
printf("insert not successful");
choice = 0;
};
break;
case 3 : delete(&first);
break;
case 4 : traverse(first);
break;
case 5:
printf("please enter a search value?\n");
scanf("%i",&mark);
choice = search(first,mark);
if (choice == -1)
{
printf("the modmark was not found\n");
}
else
{
printf("the first occurence of the mark is at the %i th index of the list",choice);
};
break;
default : printf("Invalid choice of %d \n", choice);
}; // end of switch
printinsts();
scanf("%d", &choice);
} // end of while
}
头文件llistlib.h读作
struct node {
int modmark;
struct node *next;
};
void initialise(struct node **ps);
int insert(struct node **fn);
void traverse(struct node *ps);
void delete(struct node **dn);
void finish(struct node **ps);
int search(struct node *front,int val);
我还没有能够发现任何代码中的明显问题
只需在llistlib.c
文件中包含llistlib.h
,如下所示:
#include "llistlib.h"
并使用folloeing命令进行编译:
gcc -o app llistdriver.c llistlib.c
希望这可以帮助...
第一个错误:
llistdriver.c:7: warning: return type defaults to `int'
llistdriver.c: In function `printinsts':
llistdriver.c:15: warning: control reaches end of non-void function
该功能如下:
printinsts() {}
请给这个函数一个返回类型,如果它不是void,则返回它。
其次:
llistlib.c: In function `insert':
llistlib.c:25: warning: statement with no effect
那条线是:
newnode -> next == NULL; // sets the next value to nothing
注释不正确,此行不设置任何内容,因为它使用相等运算符,而不是赋值运算符。
(这部分是一个品味的问题,但我不喜欢像这样的评论,它只是试图说出与代码本身相同的东西。在这样的情况下,它们会变得误导,你可能会读到并相信评论而不是在寻找bug时解析代码。)
然后:
llistlib.c:41: warning: control reaches end of non-void function
这又指:
int insert(struct node **fn)
{
printf("insert function\n");
struct node *newnode;
newnode = (struct node*) malloc(sizeof (struct node)); //make new node and give it memory
if (newnode == NULL) //if fsiled return to the program saying it failed
return -1;
...
}
除了-1之外,此函数没有返回。 无论发生什么,它都应该返回一些东西。
最后:
/tmp/ccqYmK3M.o:llistdriver.c:(.text+0x157): undefined reference to `_search'
因为你在结束时错过了一个结束括号();
不要因为代码编译而忽略警告。 修复错误是不够的!
您正在使用默认GCC设置进行编译,该设置“大致遵循C99标准,然后添加非标准GNU goo”。 C99标准以及当前的C标准不允许函数具有默认类型。 这就是你用-Wall得到警告的原因,返回类型必须是显式的。
printinsts() {}
无效C.您应该将此声明/定义为void printinsts (void)
而不是其他内容。
将来,请确保始终使用-std = c99或-std = c11进行编译,以确保您将代码编译为标准C语言而不是其他内容。
你的finish
功能缺少一个右括号{。 search
有一个额外的结束支撑。
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