C-编译简单的Apache Portable运行时1.5.2程序

Question

以下步骤从此处和此处，我尝试使用APR 1.5.2和APR-UTILS 1.5.4编译简单程序。这是程序的代码：

    #include <apr.h>
    #include <stdlib.h>
    int main(int argc, char *argv[]) {
        apr_pool_t *pool;
        apr_file_t *out;
        apr_initialize();
        atexit(apr_terminate());
        apr_pool_create(&pool, NULL);
        apr_file_open_stdout(&out, pool);
        apr_file_printf(out, "Hello Worldn");
        apr_pool_destroy(pool);
        return EXIT_SUCCESS;
    }

现在，当我尝试使用以下makefile进行编译时，编译器会返回错误。

makefile：

    PREFIX?=/usr/local/apr
    CFLAGS=-g -Wall -I${PREFIX}/include/apr-1
    LDFLAGS=-L${PREFIX}/apr/lib -lapr-1 -pthread -laprutil-1
    CC=clang
    .PHONY: all clean
    all: hello
    clean:
            rm -f *.o

编译器输出：

 $ make
 clang -g -Wall -I/usr/local/apr/include/apr-1  -L/usr/local/apr/apr/lib -lapr-1 -pthread -laprutil-1  hello.c   -o hello
hello.c:5:5: error: use of undeclared identifier 'apr_pool_t'
    apr_pool_t *pool;
    ^
hello.c:5:17: error: use of undeclared identifier 'pool'
    apr_pool_t *pool;
                ^
hello.c:6:5: error: unknown type name 'apr_file_t'; did you mean 'apr_size_t'?
    apr_file_t *out;
    ^~~~~~~~~~
    apr_size_t
/usr/local/apr/include/apr-1/apr.h:356:26: note: 'apr_size_t' declared here
typedef  size_t          apr_size_t;
                         ^
hello.c:8:5: warning: implicit declaration of function 'apr_initialize' is
      invalid in C99 [-Wimplicit-function-declaration]
    apr_initialize();
    ^
hello.c:9:12: warning: implicit declaration of function 'apr_terminate' is
      invalid in C99 [-Wimplicit-function-declaration]
    atexit(apr_terminate());
           ^
hello.c:9:12: warning: incompatible integer to pointer conversion passing 'int'
      to parameter of type 'void (*)(void)' [-Wint-conversion]
    atexit(apr_terminate());
           ^~~~~~~~~~~~~~~
/usr/include/stdlib.h:519:27: note: passing argument to parameter '__func' here
extern int atexit (void (*__func) (void)) __THROW __nonnull ((1));
                          ^
hello.c:11:5: warning: implicit declaration of function 'apr_pool_create' is
      invalid in C99 [-Wimplicit-function-declaration]
    apr_pool_create(&pool, NULL);
    ^
hello.c:11:22: error: use of undeclared identifier 'pool'
    apr_pool_create(&pool, NULL);
                     ^
hello.c:12:5: warning: implicit declaration of function 'apr_file_open_stdout'
      is invalid in C99 [-Wimplicit-function-declaration]
    apr_file_open_stdout(&out, pool);
    ^
hello.c:12:32: error: use of undeclared identifier 'pool'
    apr_file_open_stdout(&out, pool);
                               ^
hello.c:13:5: warning: implicit declaration of function 'apr_file_printf' is
      invalid in C99 [-Wimplicit-function-declaration]
    apr_file_printf(out, "Hello Worldn");
    ^
hello.c:14:5: warning: implicit declaration of function 'apr_pool_destroy' is
      invalid in C99 [-Wimplicit-function-declaration]
    apr_pool_destroy(pool);
    ^
hello.c:14:22: error: use of undeclared identifier 'pool'
    apr_pool_destroy(pool);
                     ^
7 warnings and 6 errors generated.
make: *** [hello] Error 1

注意：在示例中，我从中获取了一个链接-I${PREFIX}/apr/include/apr-util-1，但是APR-UTILS的安装没有创建此文件夹。

Answer 1

<apr.h>标头用于平台定义。它定义了APR可用的内容（Winapi吗？Openssl？）和标准数据类型（apr_byte_t，apr_uint32_t ..等）。它是在构建过程中由./configure自动生成的。

您需要包括的是apr_pools.h和apr_file_io.h，分别用于存储池和文件IO。

进一步的atexit(3)期望功能指针，您通过功能传递。相反，它应该说：

atexit(apr_terminate);

---

这样的错误很容易自行调试。当编译器抱怨您正在使用的库中未申报的标识符时，几乎可以肯定忘记包括适当的标题。