【发布时间】：2020-12-07 06:04:42
【问题描述】：
[在此处输入链接描述][1]我正在编写这个程序，它将启用条件编译。
当程序以这样的标准方式编译时，它可以正常工作而没有任何错误消息：
gcc -Werror -Wall -pedantic -ansi -g -c display.c -o displayStack
但是当我想使用条件编译进行编译时，我收到一条错误消息，提示我的函数在 display.c 中有隐式声明
我是这样编译的：
gcc -Werror -Wall -pedantic -ansi -g -c display.c -o displayStack -D STACK
这是我在代码中编写条件命令的方式：
#ifdef STACK
printLinkedList( stack );
#endif
这里是 stack.h 文件，其中包含 LinkedList.h 的包含，它具有 printLinkedList 的函数原型。
#ifndef STACK
#define STACK
#include "LinkedList.h"
LinkedList *createStack();
void push( LinkedList *, void * );
void *top( LinkedList * );
void *pop( LinkedList * );
void freeStack( LinkedList * );
#endif
请问这里有什么问题吗？我似乎找不到问题，因为第一条语句运行良好，但是当我添加“-D STACK”时，程序只显示错误消息。我的编译命令有问题吗？
我收到的错误消息：
display.c: In function ‘display’:
display.c:21:5: error: unknown type name ‘LinkedList’
21 | LinkedList *stack = NULL;
| ^~~~~~~~~~
display.c:22:13: error: implicit declaration of function ‘createStack’ [-Werror=implicit-function-declaration]
22 | stack = createStack();
| ^~~~~~~~~~~
display.c:22:11: error: assignment to ‘int *’ from ‘int’ makes pointer from integer without a cast [-Werror=int-conversion]
22 | stack = createStack();
| ^
display.c:47:21: error: implicit declaration of function ‘push’ [-Werror=implicit-function-declaration]
47 | push( stack, bracket );
| ^~~~
display.c:52:30: error: request for member ‘head’ in something not a structure or union
52 | if( stack->head != NULL )
| ^~
display.c:54:38: error: implicit declaration of function ‘top’ [-Werror=implicit-function-declaration]
54 | popBracket = top( stack );
| ^~~
display.c:54:36: error: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Werror=int-conversion]
54 | popBracket = top( stack );
| ^
display.c:72:42: error: implicit declaration of function ‘pop’ [-Werror=implicit-function-declaration]
72 | popBracket = pop( stack );
| ^~~
display.c:72:40: error: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Werror=int-conversion]
72 | popBracket = pop( stack );
| ^
display.c:108:17: error: implicit declaration of function ‘printLinkedList’ [-Werror=implicit-function-declaration]
108 | printLinkedList( stack );
| ^~~~~~~~~~~~~~~
display.c:147:22: error: request for member ‘head’ in something not a structure or union
147 | if( stack->head == NULL ) /* Good case */
| ^~
display.c:151:28: error: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Werror=int-conversion]
151 | popBracket = top( stack );
| ^
display.c:164:5: error: implicit declaration of function ‘freeStack’ [-Werror=implicit-function-declaration]
164 | freeStack( stack );
| ^~~~~~~~~
cc1: all warnings being treated as errors
calmen@calmen:~/Desktop/Project/BracketCheck$ vim display.h
calmen@calmen:~/Desktop/Project/BracketCheck$ gcc -Werror -Wall -pedantic -ansi -g -c display.c -o displayStack -D STACK
display.c: In function ‘display’:
display.c:21:5: error: unknown type name ‘LinkedList’
21 | LinkedList *stack = NULL;
| ^~~~~~~~~~
display.c:22:13: error: implicit declaration of function ‘createStack’ [-Werror=implicit-function-declaration]
22 | stack = createStack();
| ^~~~~~~~~~~
display.c:22:11: error: assignment to ‘int *’ from ‘int’ makes pointer from integer without a cast [-Werror=int-conversion]
22 | stack = createStack();
| ^
display.c:47:21: error: implicit declaration of function ‘push’ [-Werror=implicit-function-declaration]
47 | push( stack, bracket );
| ^~~~
display.c:52:30: error: request for member ‘head’ in something not a structure or union
52 | if( stack->head != NULL )
| ^~
display.c:54:38: error: implicit declaration of function ‘top’ [-Werror=implicit-function-declaration]
54 | popBracket = top( stack );
| ^~~
display.c:54:36: error: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Werror=int-conversion]
54 | popBracket = top( stack );
| ^
display.c:72:42: error: implicit declaration of function ‘pop’ [-Werror=implicit-function-declaration]
72 | popBracket = pop( stack );
| ^~~
display.c:72:40: error: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Werror=int-conversion]
72 | popBracket = pop( stack );
| ^
display.c:108:17: error: implicit declaration of function ‘printLinkedList’ [-Werror=implicit-function-declaration]
108 | printLinkedList( stack );
| ^~~~~~~~~~~~~~~
display.c:147:22: error: request for member ‘head’ in something not a structure or union
147 | if( stack->head == NULL ) /* Good case */
| ^~
display.c:151:28: error: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Werror=int-conversion]
151 | popBracket = top( stack );
| ^
display.c:164:5: error: implicit declaration of function ‘freeStack’ [-Werror=implicit-function-declaration]
164 | freeStack( stack );
| ^~~~~~~~~
cc1: all warnings being treated as errors
可以在此处的文件夹中找到这些文件。 [1]：https://github.com/Calmen00-code/BracketCheck
【问题讨论】：
-
我们只能猜测而没有看到您应该提供的complete minimal verifiable example。并提供exact错误信息。但听起来在代码中调用它的点之前没有
printLinkedList函数的定义或原型。 -
它与条件编译本身没有任何关系。这只是意味着您通过添加
-DSTACK启用的代码中存在错误。如果没有-DSTACK，代码将被忽略，因此编译器看不到其中的任何错误。您没有显示实际的错误消息（在寻求帮助时您应该始终剪切/粘贴实际的错误消息），但很可能它说printLinkedList是问题所在。在 Google 上搜索错误“隐式声明”的含义以及如何解决。 -
代码需要作为可验证的最小示例出现在问题中，而不是作为外部链接。无论如何，我认为我们已经相当清楚地表明了可能的错误是什么。你明白上面所说的吗 - 函数需要在调用之前声明。
-
嗨，我在问题中包含了 github 链接。我不知道为什么会发生隐式声明，因为我已经添加了我的函数声明，并且当我在没有条件编译的情况下编译它时它可以正常工作而不会显示错误消息。希望我已经把问题说清楚了..提前谢谢！
-
谢谢@kaylum。是的，我知道函数原型设计必须在函数定义之前。我已经这样做了，但它似乎仍然显示错误消息。
标签： c conditional-compilation makefile