读文章笔记：Creating a Shared Library

程序的目的是，提供C或C++的接口，判断一个字符串是否为回文。

pal.h

int is_palindrome (char * word);

pal.hpp

class palindrome {
public:
    palindrome ();
    bool is_palindrome (char * word);
};

pal.cpp

#include "pal.hpp"
#include <string.h>

using namespace std;

extern "C" int is_palindrome (char * word)
{
    int ret = 1;
    char * p = word;
    int len = strlen (word);
    char * q = &word[len-1];

    for (int i = 0 ; i < len ; i++, p++, q--)
    {
        if (*p != *q)
        {
            ret = 0;
        }
    }
    return ret;
}

bool palindrome::is_palindrome (char * word)
{
    bool ret = true;
    char * p = word;
    int len = strlen (word);
    char * q = &word[len-1];

    for (int i = 0 ; i < len ; i++, p++, q--)
    {
        if (*p != *q)
        {
            ret = false;
        }
    }
    return ret;
}

编译出 pal.o：

# g++ -fPIC pal.cpp
# ls
pal.cpp  pal.h  pal.o

生成 libpal.so：

# ld -shared pal.o -o libpal.so
# ls
libpal.so  pal.cpp  pal.h  pal.o

# sudo mv libpal.so /usr/lib64
# sudo ldconfig
# sudo ldconfig -p | grep libpal
        libpal.so (libc6,x86-64) => /lib64/libpal.so

C++ 程序

接下来，我们创建一个 main.cpp 来调用这个共享库中的函数：

main.cpp

#include "pal.hpp"
#include <iostream>

using namespace std;

int main()
{
    palindrome a;

    while (1)
    {
        char buffer[64] = {0};
        cin >> buffer;

        if (a.is_palindrome(buffer))
        {
            cout << "Word is a palindrome" << endl;
        }
        else
        {
            cout << "Word is not a palindrome" << endl;
        }
    }

    return 0;
}

生成可执行文件 a.out :

# g++ main.cpp -lpal

$ ./a.out
ada
Word is a palindrome
team
Word is not a palindrome

C 程序

main.c

#include "pal.h"
#include <stdio.h>
#include <unistd.h>
#include <string.h>

int main()
{
    while (1)
    {
        char buffer[64] = {0};
        read(STDIN_FILENO, buffer, 60);

        int len = strlen(buffer);
        buffer[len-1] = 0;

        if (is_palindrome(buffer))
        {
            printf ("Word is a palindrome\n");
        }
        else
        {
            printf ("Word is not a palindrome\n");
        }
    }

    return 0;
}

生成可执行文件 b.out :

# gcc main.c -lpal -o b.out

$ ./b.out
ada
Word is a palindrome
team
Word is not a palindrome

参考文章链接

1 Creating a Shared Library
2 Installing and Accessing Shared Libraries
3 C++ Dynamic Shared Library on Linux