学习Json记录

第一次写csdn，记录一下。

学习EasyDevice时，了解到EasyDevice使用HTTP协议承载Json数据在设备与服务器之间、及服务器与客户端之间进行数据交互，同时也看到许多网络协议也是基于Json格式的，逐认识到Json应用的广泛性，看来得认识下Json了。

来看下较W3C的教程

JSON：JavaScript 对象表示法（JavaScript Object Notation）。

JSON 是存储和交换文本信息的语法。类似 XML。

JSON 比 XML 更小、更快，更易解析。

JSON 语法是 JavaScript 语法的子集。

JSON 语法规则

JSON 语法是 JavaScript 对象表示法语法的子集。

• 数据在名称/值对中
• 数据由逗号分隔
• 花括号保存对象
• 方括号保存数组

JSON 名称/值对

JSON 数据的书写格式是：名称/值对。

名称/值对包括字段名称（在双引号中），后面写一个冒号，然后是值：

"firstName" : "John"

这很容易理解，等价于这条 JavaScript 语句：

firstName = "John"

JSON 值

JSON 值可以是：

• 数字（整数或浮点数）
• 字符串（在双引号中）
• 逻辑值（true 或 false）
• 数组（在方括号中）
• 对象（在花括号中）
• null

JSON 对象

JSON 对象在花括号中书写：

对象可以包含多个名称/值对：

{ "firstName":"John" , "lastName":"Doe" }

这一点也容易理解，与这条 JavaScript 语句等价：

firstName = "John"lastName = "Doe"

JSON 数组

JSON 数组在方括号中书写：

数组可包含多个对象：

{"employees": [{ "firstName":"John" , "lastName":"Doe" },{ "firstName":"Anna" , "lastName":"Smith" },{ "firstName":"Peter" , "lastName":"Jones" }]}

在上面的例子中，对象 "employees" 是包含三个对象的数组。每个对象代表一条关于某人（有姓和名）的记录。

自己试着写一个Json文件！

==================================  example1_dvr.json =================================={"System" : {"Hardware" : "DVR_HW_v1.0","Software" : "DVR_SW_v1.0","CameraNum" : 4,"HasPtz" : true,"HasEthernet" : true,"HasWiFi" : false,"HasGPS" : true},"Config" : {"Camera" : [{"Video" : {"EncType" : "H264","EncSize" : "1280x960","EncFrameRate" : 29.5,"EncMode" : "CBR","EncBitRate" : 2048},"Audio" : {"EncType" : "G711A"}},{"Video" : {"EncType" : "H264","EncSize" : "1280x960","EncFrameRate" : 29.5,"EncMode" : "CBR","EncBitRate" : 2048},"Audio" : {"EncType" : "G711A"}},{"Video" : {"EncType" : "H264","EncSize" : "1280x960","EncFrameRate" : 29.5,"EncMode" : "CBR","EncBitRate" : 2048},"Audio" : {"EncType" : "G711A"}},{"Video" : {"EncType" : "H264","EncSize" : "1280x960","EncFrameRate" : 29.5,"EncMode" : "CBR","EncBitRate" : 2048},"Audio" : {"EncType" : "G711A"}}],"PTZ" : {"Serial" : "/dev/ttyAMA2","Baudrate" : 9600,"Protocol" : "PolcoD","CameraAddr" : [1, 2, 3, 4]},"GPS" : {"Serial" : "/dev/ttyAMA1","Baudrate" : 9600,"Protocal" : "Blox"}},"Log" : [{"Time" : "09:26:23", "Tag" : "UserLogin", "Description" : "ip:183.39.231.137"},{"Time" : "09:37:30", "Tag" : "UserLogout", "Description" : "ip:183.39.231.137"},{"Time" : "09:51:36", "Tag" : "UserLogin", "Description" : "ip:121.196.220.153"},{"Time" : "09:52:32", "Tag" : "UserLogout", "Description" : "ip:121.196.220.153"},{"Time" : "11:56:18", "Tag" : "UserLogin", "Description" : "ip:121.196.220.153"},{"Time" : "11:56:53", "Tag" : "UserLogout", "Description" : "ip:121.196.220.153"},{"Time" : "19:26:23", "Tag" : "UserLogin", "Description" : "ip:183.39.231.137"},{"Time" : "19:37:30", "Tag" : "UserLogout", "Description" : "ip:183.39.231.137"},{"Time" : "19:51:36", "Tag" : "UserLogin", "Description" : "ip:121.196.220.153"},{"Time" : "21:56:53", "Tag" : "UserLogout", "Description" : "ip:121.196.220.153"}]}================================== end ==================================

在网上找个在线Json解析网站，将上述Json贴上去，验证通过^_^!!!

使用cJson库解析再打印下

==================================  example1_dvr.c ==================================#include <stdio.h>#include <stdlib.h>#include <string.h>#include <errno.h>#include <cJSON.h>int main(int argc, char *argv[]){FILE *fp = fopen(argv[1], "r");char *pJsonFileBuf = NULL;int iJsonFileLen = 0;cJSON *pJsonObj = NULL;char *pJsonPrintBuf = NULL;if (!fp) {fprintf(stderr, "fopen fail: %s\n", strerror(errno));return -1;}fseek(fp, 0L, SEEK_END);iJsonFileLen = ftell(fp);fseek(fp, 0L, SEEK_SET);pJsonFileBuf = (char*) calloc(1, iJsonFileLen + 1);if (!pJsonFileBuf) {fprintf(stderr, "Calloc for JsonFileBuf fail: %s\n", strerror(errno));return -1;}fread(pJsonFileBuf, iJsonFileLen, 1, fp);pJsonObj = cJSON_Parse(pJsonFileBuf);if (!pJsonObj) {fprintf(stderr, "cJSON_Parse fail: %s\n", cJSON_GetErrorPtr());return -1;}pJsonPrintBuf = cJSON_Print(pJsonObj);if (!pJsonPrintBuf) {fprintf(stderr, "cJSON_Print fail: %s\n", cJSON_GetErrorPtr());return -1;}fprintf(stderr, "JSON format is right !!!\n");printf("%s", pJsonPrintBuf);fflush(stdout);fprintf(stderr, "\n");free(pJsonPrintBuf);cJSON_Delete(pJsonObj);free(pJsonFileBuf);fclose(fp);return -1;}==================================  end ==================================

再来个运行截图

解析正确，cJson打印格式跟手写不一样哦。先学到这吧，用到再继续熟悉，哈哈