包括静态库中的头文件 [英] Including header file from static library

问题描述

我正在测试C静态库和程序. 库代码位于我项目的子目录"foo"中，包含以下文件:

I am making a test setup of a C static library and program. The library code, located in a subdirectory 'foo' of my project, contains the following files:

foo/foo.c:

#include <stdio.h>
void foo(void) {
    printf("something");
}

foo/foo.h:

#ifndef foo_h__
#define foo_h__
extern void foo(void);
#endif

我的程序代码如下:

test.c:

#include "foo.h"
int main() {
    foo();
    return 0;
}

我有一个名为"build"的构建脚本，其中包含以下内容:

I have a build script, called 'build', which contains the following:

内部版本:

#!/bin/bash
gcc -c -Wall -Werror foo/foo.c
ar rcs libfoo.a foo.o
gcc -static -o test test.c libfoo.a # I have also tried -L. -lfoo

但是当我运行build时，它给了我以下错误:

But when I run build, it gives me the following error:

test.c:1:17: fatal error: foo.h: No such file or directory
  #include "foo.h"
                  ^
Compilation terminated

但是，当我省略#include行时，它确实可以工作，但是如果可以在我的静态库中使用头文件，我会更喜欢.我在做什么错了，我该如何解决?

It does, however, work when I omit the #include line, but I would prefer if I could use header files in my static libraries. What am I doing wrong, and how can I fix it?

推荐答案

标头未存储在库中.标头与库分开存储.库包含目标文件；标头不是目标文件.默认情况下，Unix系统上的标准标头存储在/usr/include中-例如，通常会找到/usr/include/stdio.h和/usr/include/string.h和/usr/include/stdlib.h.默认情况下，库存储在/usr/lib中(但是您也可以在/lib中找到某些库).通常，编译器也被配置为也可以在其他地方查找.一个常见的替代位置在/usr/local下，因此/usr/local/include表示标题，而/usr/local/lib表示库.还要注意，单个库可能有许多定义服务的标头.默认库是一个示例.它具有与<stdio.h>，<string.h>，<stdlib.h>和许多其他标头中的功能相对应的功能.

Headers are not stored in libraries. Headers are stored separately from libraries. Libraries contain object files; headers are not object files. By default, standard headers on a Unix system are stored in /usr/include — you'll normally find /usr/include/stdio.h and /usr/include/string.h and /usr/include/stdlib.h, for example. By default, libraries are stored in /usr/lib (but you may also find some in /lib). Often, compilers are configured to look in some other places too. One common alternative location is under /usr/local, so /usr/local/include for headers and /usr/local/lib for libraries. Note, too, that a single library may have many headers defining the services. The default library is an example. It has the functions corresponding to those found in <stdio.h>, <string.h>, <stdlib.h> and many other headers too.

查看您的代码:

1. 如果头文件位于./foo/foo.h中，则需要编写:

#include "foo/foo.h"

或者，如果您继续使用#include "foo.h"，则需要使用以下参数指定在编译器命令行中查找标头的位置:

Or if you continue to use #include "foo.h", you need to specify where to find the header on the compiler command line with the argument:

gcc -Ifoo -o test test.c -L. -lfoo

我故意排除了-static；仅当在静态库和共享库之间进行选择时才有必要，但是您只有libfoo.a，因此链接器仍将使用该库.

I deliberately excluded the -static; it's only necessary when there's a choice between a static and a shared library, but you only have libfoo.a, so the linker will use that anyway.

请注意，问题是编译错误，而不是链接错误.如果将程序构建分为两个步骤，这将更加清楚:(1)创建test.o和(2)链接程序:

Note that the problem is a compilation error, not a linking error. This would be clearer if you split the program building into two steps: (1) create test.o and (2) link program:

gcc -c -Ifoo test.c
gcc -o test test.o -L. -lfoo

您的页眉防护出现故障.您原来有(但是已经更新了问题，所以不再存在此错字):

Your header guard is faulty. You originally had (but have updated the question so this typo is no longer present):

#ifndef foo_h__
#define foo_h_

您需要:

#ifndef foo_h__
#define foo_h__

两行中的宏名称必须相同.请注意，在这种情况下，拼写错误几乎是无害的-但是在Mac OS X上，clang(伪装为gcc)确实对此提供了警告(尽管我在进行任何编译之前就已经发现了它).在某些其他情况下，您将无法获得标头保护程序旨在提供的保护.

The macro names must be the same in both lines. Note that in this case, the misspelling is mostly harmless — but on Mac OS X, clang (masquerading as gcc) did give a warning about it (though I'd spotted it before I did any compilation). In some other cases, you wouldn't get the protection that the header guards are designed to provide.

./foo/foo.h:1:9: warning: 'foo_h__' is used as a header guard here, followed by #define of a
      different macro [-Wheader-guard]
#ifndef foo_h__
        ^~~~~~~
./foo/foo.h:2:9: note: 'foo_h_' is defined here; did you mean 'foo_h__'?
#define foo_h_
        ^~~~~~
        foo_h__
1 warning generated.

您可能会合理地想知道:

You might legitimately wonder:

• 如果在编译test.c时需要-Ifoo，为什么在编译foo/foo.c时没有必要?

• If I need -Ifoo when compiling test.c, why wasn't it necessary when compiling foo/foo.c?

好问题！

1. 这不会损害foo/foo.c
的编译
2. GCC在找到翻译单元源代码的目录中查找标头(因此，编译foo/foo.c时，它在foo目录中查找反而包含为#include "foo.h"的标头.
3. 源文件foo/foo.c也应该包含foo.h；这样做非常重要，因为这就是编译器提供必要的交叉检查以确保一致性的方式.如果您编写了#include "foo.h"，则编译将按照说明进行.如果您(在foo/foo.c中)编写了#include "foo/foo.h"，则用于创建foo.o的命令行将需要-I.，以便可以找到标头.

1. It would not have hurt the compilation of foo/foo.c
2. GCC looks for headers in the directory where the source code of the translation unit is found (so, when compiling foo/foo.c, it looks in foo directory for headers included as #include "foo.h" anyway.
3. The source file foo/foo.c should have included foo.h too; it is very important that it does as that is how the compiler provides the cross-checking necessary to ensure consistency. If you had written #include "foo.h", the compilation would work as described. If you wrote (in foo/foo.c) #include "foo/foo.h", then the command line for creating foo.o would have needed -I. so the header could be found.

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