CentOS 7 使用cJSON 库-编程知识

什么是JSON

JSON是一种轻量级的数据交换格式，可读性强、编写简单。键值对组合编写规则，键名使用双引号包裹，冒号：分隔符后面紧跟着数值，有两种常用的数据类型是对象和数组。

对象：使用花括号{}包裹起来的内容，数据结构{“key1”: “value1”, “key2”:“value2” …}，key为对象的属性，value为对象的值。

数值：使用中括号[]包裹起来的内容，数据结构{“key”: [“value1”, “value2”, “value3” …]}。

CentOS 7 安装cJSON 库

cJSON Github 地址：https://github.com/DaveGamble/cJSON

步骤1：首先，你需要下载cJSON的源代码。你可以从https://github.com/DaveGamble/cJSON或者源代码官方网站下载。并上传至/usr/local/source_code/

步骤2：下载完成后，需要将源代码解压，可以使用以下命令：

[root@localhost source_code]# tar -zxvf cJSON-1.7.15.tar.gz

步骤3：解压后，切换到源代码目录：

[root@localhost source_code]# cd cJSON-1.7.15

步骤4：生成cJSON动态/静态库，执行如下指令：

[root@localhost cJSON-1.7.15]# mkdir build
[root@localhost cJSON-1.7.15]# cd build/
[root@localhost build]# cmake ..
CMake Deprecation Warning at CMakeLists.txt:2 (cmake_minimum_required):Compatibility with CMake < 2.8.12 will be removed from a future version ofCMake.Update the VERSION argument <min> value or use a ...<max> suffix to tellCMake that the project does not need compatibility with older versions.-- The C compiler identification is GNU 8.3.1
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
******
[root@localhost build]# make && make install
[  2%] Building C object CMakeFiles/cjson.dir/cJSON.c.o
[  4%] Linking C shared library libcjson.so
[  4%] Built target cjson
[  6%] Building C object CMakeFiles/cJSON_test.dir/test.c.o
[  8%] Linking C executable cJSON_test
[  8%] Built target cJSON_test
[ 11%] Building C object tests/CMakeFiles/unity.dir/unity/src/unity.c.o
[ 13%] Linking C static library libunity.a
[ 13%] Built target unity
[ 15%] Building C object tests/CMakeFiles/print_number.dir/print_number.c.o
[ 17%] Linking C executable print_number
-- 省略--
[100%] Built target fuzz_main
Install the project...
-- Install configuration: ""
-- Installing: /usr/local/include/cjson/cJSON.h
-- Installing: /usr/local/lib64/pkgconfig/libcjson.pc
-- Installing: /usr/local/lib64/libcjson.so.1.7.15
-- Installing: /usr/local/lib64/libcjson.so.1
-- Installing: /usr/local/lib64/libcjson.so
-- Installing: /usr/local/lib64/cmake/cJSON/cjson.cmake
-- Installing: /usr/local/lib64/cmake/cJSON/cjson-noconfig.cmake
-- Installing: /usr/local/lib64/cmake/cJSON/cJSONConfig.cmake
-- Installing: /usr/local/lib64/cmake/cJSON/cJSONConfigVersion.cmake

遇到的问题及解决办法

编译执行./test_cjson,提示如下截图错误信息：

[root@localhost cJSON_demo]# ./test_cjson
./test_cjson: error while loading shared libraries: libcjson.so.1: cannot open shared object file: No such file or directory

从报错的原因上看，本机上没有找到cJOSN类库的静态库/动态库libcjson.so。

首先检查/usr/local/lib 和/usr/local/include 目录中是否包含cjson 静态或动态库，可以执行如下指令：

ls /usr/local/lib | grep cjson
ls /usr/local/include | grep cjson

从上面分组查询结果可知：cjson 没有在/usr/local/lib 库中生成cjson 静态/动态库链接。

再次查看cJOSN 在执行make && make install 指令时，对应cJSON 静态/动态库生成链接存放目录地址。

从上述截图可知cJSON 静态/动态库被安装到了/usr/local/lib64 目录中。

将/usr/local/lib64 目录添加至本机静态/动态库链接目录文件中，执行如下指令：

[root@localhost cJSON_demo]# cat /etc/ld.so.conf.d/usr-libs.conf
/usr/local/lib
[root@localhost cJSON_demo]# vi /etc/ld.so.conf.d/usr-libs.conf
[root@localhost ~]#  cat /etc/ld.so.conf.d/usr-libs.conf
/usr/local/lib
/usr/local/lib64
[root@localhost cJSON_demo]# sudo ldconfig

再次编译执行./test_cjson, Main 函数正确输出。

cJSON快速入门

在/usr/local/source_code 新增 cJSON_demo目录并新增test_cjson.c 文件，文件内容如下：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <cjson/cJSON.h>int main()
{cJSON *json = NULL;cJSON *node = NULL;cJSON *tnode = NULL;cJSON *tnode2 = NULL;char *json_data = NULL;int i, j, size, size2;char *data = "{\"serialNumber\":\"212089842348362300\", \\"cellularInfo\":\[\{\"name\":\"ethernet0/0/1\",\\"switch\":\"0\"},\{\"name\":\"ethernet0/0/2\",\\"switch\":\"1\"},\{\"name\":\"ethernet0/0/3\",\\"switch\":\"0\"}\],\\"family\":[\"father\",\"mother\",\"brother\",\"sister\",\"somebody\"]\}";json = cJSON_Parse(data);json_data = cJSON_Print(json);printf("data: %s\n", json_data);free(json_data);node = cJSON_GetObjectItem(json,"serialNumber");if(node == NULL)printf("serialNumber: no\n");elseprintf("serialNumber: ok\n");node = cJSON_GetObjectItem(json, "family");if (node == NULL)printf("family: no\n");elseprintf("family: ok\n");if (node->type == cJSON_Array){printf("family array size is %d\n", cJSON_GetArraySize(node));size = cJSON_GetArraySize(node);for (i=0; i<size; i++){tnode = cJSON_GetArrayItem(node, i);if (tnode->type == cJSON_String)printf("%d: %s\n", i, tnode->valuestring);elseprintf("node type is not string, value = %d\n", tnode->type);}}node = cJSON_GetObjectItem(json, "cellularInfo");if(node == NULL)printf("cellularInfo: no\n");elseprintf("cellularInfo: ok\n");if (node->type == cJSON_Array){printf("cellularInfo array size is %d\n", cJSON_GetArraySize(node));size = cJSON_GetArraySize(node);for (i=0; i<size; i++){tnode = cJSON_GetArrayItem(node, i);if (tnode->type == cJSON_String)printf("%d: %s\n", i, tnode->valuestring);else if (tnode->type == cJSON_Object){size2 = cJSON_GetArraySize(tnode);for (j=0; j<size2; j++){tnode2 = cJSON_GetArrayItem(tnode, j);if (tnode2->type == cJSON_String)printf("%d-%d: %s\n", i, j, tnode2->valuestring);elseprintf("tnod2 type is err\n");}}elseprintf("node type is not string, value = %d\n", tnode->type);}}cJSON_Delete(json);return 0;
}

编译源码并执行：

[root@localhost cJSON_demo]# gcc -o test_cjson test_cjson.c -lcjson
[root@localhost cJSON_demo]# ./test_cjson
data: {"serialNumber": "212089842348362300","cellularInfo": [{"name": "ethernet0/0/1","switch":       "0"}, {"name": "ethernet0/0/2","switch":       "1"}, {"name": "ethernet0/0/3","switch":       "0"}],"family":       ["father", "mother", "brother", "sister", "somebody"]
}
serialNumber: ok
family: ok
family array size is 5
0: father
1: mother
2: brother
3: sister
4: somebody
cellularInfo: ok
cellularInfo array size is 3
0-0: ethernet0/0/1
0-1: 0
1-0: ethernet0/0/2
1-1: 1
2-0: ethernet0/0/3
2-1: 0