“某事”的多重定义
在“my_header.h”中我定义了
FILE *f;
char *logfile = "my_output.txt";
#define OPEN_LOG f = fopen(logfile, "a")
#define CLOSE_LOG fclose(f)
，在“my_source.c”中，我以这种方式使用它
#include "my_header.h"
....
OPEN_LOG;
fprintf(f, "some strings\n");
CLOSE_LOG;
但是链接器说
my_source.o:(.data+0x0): multiple definition of `logfile'
How can I fix that?
In "my_header.h" I defined
FILE *f;
char *logfile = "my_output.txt";
#define OPEN_LOG f = fopen(logfile, "a")
#define CLOSE_LOG fclose(f)
and in "my_source.c", I used it in this way
#include "my_header.h"
....
OPEN_LOG;
fprintf(f, "some strings\n");
CLOSE_LOG;
However the linker says
my_source.o:(.data+0x0): multiple definition of `logfile'
How can I fix that?
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一如既往，不要在头文件中定义变量。因为每次你
#include该头文件时，该变量都会被重新定义（记住#include==“有效地复制和粘贴”），导致您看到的链接器错误。As always, don't define variables in your header file. Because every time you
#includethat header file, that variable will be re-defined (remember that#include== "copy and paste", effectively), leading to the linker error that you're seeing.您应该创建一个新文件 (
my_stuff.c)，并在其中包含以下内容：.c 文件定义变量。然后更改标头以使用此内容而不是定义：
这使其成为声明。现在一切应该可以工作了，但是您必须编译额外的模块，并将其包含在链接阶段。 （具体操作取决于您的开发工具。）
You should create a new file (
my_stuff.c), and have this in there:The .c file defines the variable. Then change the header to have this instead of the definition:
This makes it a declaration. Now things should work, but you have to compile the extra module, and include it in the link phase. (Details of doing that depend on your development tools.)