头文件中const变量的多个定义

Mateus Pires 发表于 Dev

马修·皮雷斯（Matthew Pires）

我在flag.h中定义了一些常量，因此link.c和linkedlist.h可以使用它。但是当我编译时：

lang -Wall main.c link.clinkedlist.c

我得到以下

/tmp/linkedlist-o2mcAI.o:(.rodata+0x0）：“ VARIABLE_NAME ”的多个定义

/tmp/link-oXhyfE.o:(.rodata+0x0）：首先在此处定义

从所有变量flag.h中使用link.c和linkedlist.c，并在最后：

铛：错误：链接器命令失败，退出代码为1（使用-v查看调用）

main.c，flag.h，link.h，link.c，linkedlist.h和linkedlist.c的示例代码：

main.c

#include <stdio.h>
#include "linkedlist.h"

int main(void) {
    LinkedList* list = LinkedList_new();
}

标记

#ifndef FLAG_H_
#define FLAG_H_

#include <limits.h>

#define FALSE 0
#define TRUE 1

const int OK = 1;
const int ERROR = -1;
const int FLAG = 0;

// other constants

#endif

链接

#ifndef LINK_H_
#define LINK_H_

typedef struct Link {
    int value;
    struct Link* next;
} Link;

Link* Link_new(int value);

int useExample(int value);

// other methods

#endif

链接

#include <stdio.h>
#include <stdlib.h>

#include "link.h"
#include "flag.h"

Link* Link_new(int value)
{
    Link* link = malloc(sizeof(Link));
    link->value = value;
    link->next = NULL;
    return link;
}

useExample(int value)
{
    if (value == 0) {
        return OK; // defined in flag.h
    } else {
        return FLAG; // defined in flag.h
    }
}

// other methods

链表

#ifndef LINKEDLIST_H_
#define LINKEDLIST_H_

#include "link.h"

typedef struct LinkedList {
    Link* first;
    unsigned int size;
} LinkedList;

LinkedList* LinkedList_new();

int anotherUseExample(int value);

// other methods

#endif

链表

#include <stdio.h>
#include <stdlib.h>

#include "linkedlist.h"
#include "flag.h"

LinkedList* LinkedList_new() {
    LinkedList* list = malloc(sizeof(LinkedList));
    list->first = NULL;
    list->size = 0;
    return list;
}

anotherUseExample(int value)
{
    if (value == 0) {
        return FLAG; // defined in flag.h
    } else {
        return ERROR; // defined in flag.h
    }
}

// other methods

那么，如何可以使用flag.h在link.c和linkedlist.c没有出现多重定义？

还有...我编码头文件和编译的方式正确吗？

完整的输出包括-v：

clang version 3.3 (tags/RELEASE_33/rc3)
Target: i386-redhat-linux-gnu
Thread model: posix
 "/usr/bin/clang" -cc1 -triple i386-redhat-linux-gnu -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -main-file-name main.c -mrelocation-model static -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases -fuse-init-array -target-cpu pentium4 -target-linker-version 2.23.52.0.1 -v -resource-dir /usr/bin/../lib/clang/3.3 -internal-isystem /usr/local/include -internal-isystem /usr/bin/../lib/clang/3.3/include -internal-externc-isystem /usr/include -internal-externc-isystem /usr/lib/gcc/i686-redhat-linux/4.8.1/include -Wall -fdebug-compilation-dir /home/jharvard/Desktop/Code/LinkedList -ferror-limit 19 -fmessage-length 80 -mstackrealign -fobjc-runtime=gcc -fobjc-default-synthesize-properties -fdiagnostics-show-option -fcolor-diagnostics -backend-option -vectorize-loops -o /tmp/main-JmZTmN.o -x c main.c
clang -cc1 version 3.3 based upon LLVM 3.3 default target i386-redhat-linux-gnu
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/bin/../lib/clang/3.3/include
 /usr/include
 /usr/lib/gcc/i686-redhat-linux/4.8.1/include
End of search list.
 "/usr/bin/clang" -cc1 -triple i386-redhat-linux-gnu -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -main-file-name link.c -mrelocation-model static -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases -fuse-init-array -target-cpu pentium4 -target-linker-version 2.23.52.0.1 -v -resource-dir /usr/bin/../lib/clang/3.3 -internal-isystem /usr/local/include -internal-isystem /usr/bin/../lib/clang/3.3/include -internal-externc-isystem /usr/include -internal-externc-isystem /usr/lib/gcc/i686-redhat-linux/4.8.1/include -Wall -fdebug-compilation-dir /home/jharvard/Desktop/Code/LinkedList -ferror-limit 19 -fmessage-length 80 -mstackrealign -fobjc-runtime=gcc -fobjc-default-synthesize-properties -fdiagnostics-show-option -fcolor-diagnostics -backend-option -vectorize-loops -o /tmp/link-FtygcZ.o -x c link.c
clang -cc1 version 3.3 based upon LLVM 3.3 default target i386-redhat-linux-gnu
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/bin/../lib/clang/3.3/include
 /usr/include
 /usr/lib/gcc/i686-redhat-linux/4.8.1/include
End of search list.
 "/usr/bin/clang" -cc1 -triple i386-redhat-linux-gnu -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -main-file-name linkedlist.c -mrelocation-model static -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases -fuse-init-array -target-cpu pentium4 -target-linker-version 2.23.52.0.1 -v -resource-dir /usr/bin/../lib/clang/3.3 -internal-isystem /usr/local/include -internal-isystem /usr/bin/../lib/clang/3.3/include -internal-externc-isystem /usr/include -internal-externc-isystem /usr/lib/gcc/i686-redhat-linux/4.8.1/include -Wall -fdebug-compilation-dir /home/jharvard/Desktop/Code/LinkedList -ferror-limit 19 -fmessage-length 80 -mstackrealign -fobjc-runtime=gcc -fobjc-default-synthesize-properties -fdiagnostics-show-option -fcolor-diagnostics -backend-option -vectorize-loops -o /tmp/linkedlist-n0zF1a.o -x c linkedlist.c
clang -cc1 version 3.3 based upon LLVM 3.3 default target i386-redhat-linux-gnu
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/bin/../lib/clang/3.3/include
 /usr/include
 /usr/lib/gcc/i686-redhat-linux/4.8.1/include
End of search list.
 "/usr/bin/ld" --eh-frame-hdr -m elf_i386 -dynamic-linker /lib/ld-linux.so.2 -o a.out /usr/lib/gcc/i686-redhat-linux/4.8.1/../../../crt1.o /usr/lib/gcc/i686-redhat-linux/4.8.1/../../../crti.o /usr/lib/gcc/i686-redhat-linux/4.8.1/crtbegin.o -L/usr/lib/gcc/i686-redhat-linux/4.8.1 -L/usr/lib/gcc/i686-redhat-linux/4.8.1/../../.. -L/lib -L/usr/lib /tmp/main-JmZTmN.o /tmp/link-FtygcZ.o /tmp/linkedlist-n0zF1a.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/i686-redhat-linux/4.8.1/crtend.o /usr/lib/gcc/i686-redhat-linux/4.8.1/../../../crtn.o
/tmp/linkedlist-n0zF1a.o:(.rodata+0x4): multiple definition of `ERROR_indexOutOfBounds'
/tmp/link-FtygcZ.o:(.rodata+0x4): first defined here
/tmp/linkedlist-n0zF1a.o:(.rodata+0x8): multiple definition of `ERROR_invalidArgument'
/tmp/link-FtygcZ.o:(.rodata+0x8): first defined here
/tmp/linkedlist-n0zF1a.o:(.rodata+0x10): multiple definition of `FLAG_notFound'
/tmp/link-FtygcZ.o:(.rodata+0x10): first defined here
/tmp/linkedlist-n0zF1a.o:(.rodata+0xc): multiple definition of `FLAG_undefined'
/tmp/link-FtygcZ.o:(.rodata+0xc): first defined here
/tmp/linkedlist-n0zF1a.o:(.rodata+0x0): multiple definition of `OK'
/tmp/link-FtygcZ.o:(.rodata+0x0): first defined here
clang: error: linker command failed with exit code 1 (use -v to see invocation)

伊丹·阿里（Idan Arye）

#includeC中的指令只是从头文件复制文本。这意味着，当您同时编译link.c和时linkedlist.c，from中的常量定义flag.h将被复制到两者中，并且所有这些常量现在都在link.o和linkedlist.o中定义了。当您链接程序时，您将获得一个名称，您将获得一个多定义错误。

您需要从定义中拆分声明，并flag.c在其中定义const int OK = 1;等的位置创建一个文件，然后flag.h与const int OK;etc一起使用。这样，常量将被编译为单个目标文件--flag.o您将不会得到链接时出现多个定义错误。

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编辑于2021-02-10

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