cJSON移植到STM32F系列单片机

项目中用到JSON接收网络数据，具体是STM32串口接收JSON数据，提取需要的内容。本来KEIL MDK是自带JSON的，但是我不习惯使用KEIL自带的那些第三方的东西，很杂乱的感觉。cJSON的移植比较简单，一下子就可以搞定。

1、下载源文件。

http://sourceforge.net/projects/cjson/

只需要两个文件cJSON.c，cJSON.h;下载的包里面还有一个test.c，里面是测试的例子。

http://www.json.org/json-zh.html

这个是JSON的中文说明，明了清晰。

2、实现内存管理接口。

这个可以直接使用原子的Malloc.c,Malloc.h，并修改合适的管理内存大小MEM_MAX_SIZE。

3、修改源代码

将cJSON.c里面所有的malloc何free为自定义内存管理函数。注意是所有。

4、测试。

下载的包里面test.c里面有很多例子，可以拿来测试。

4.1

这个是解析JSON字符串的：

/* Parse text to JSON, then render back to text, and print! */
void doit(char *text)
{char *out;cJSON *json;json=cJSON_Parse(text);if (!json) {printf("Error before: [%s]\n",cJSON_GetErrorPtr());}else{out=cJSON_Print(json);cJSON_Delete(json);printf("%s\n",out);myfree(out);}
}

使用PC串口根据和STM32的串口测试一段字符串：

接收的文本为

{"a":	"1","b":	{"a1":	1.100000}
}

故意发送弄个不合规范的试试：

4.2

还有生成JSON的代码：

/* Used by some code below as an example datatype. */
struct record {const char *precision;double lat,lon;const char *address,*city,*state,*zip,*country; };/* Create a bunch of objects as demonstration. */
void create_objects()
{cJSON *root,*fmt,*img,*thm,*fld;char *out;int i;    /* declare a few. *//* Our "days of the week" array: */const char *strings[7]={"Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"};/* Our matrix: */int numbers[3][3]={{0,-1,0},{1,0,0},{0,0,1}};/* Our "gallery" item: */int ids[4]={116,943,234,38793};/* Our array of "records": */struct record fields[2]={{"zip",37.7668,-1.223959e+2,"","SAN FRANCISCO","CA","94107","US"},{"zip",37.371991,-1.22026e+2,"","SUNNYVALE","CA","94085","US"}};/* Here we construct some JSON standards, from the JSON site. */printf("\r\n ***start***%d%% \r\n",mem_perused());/* Our "Video" datatype: */root=cJSON_CreateObject();    cJSON_AddItemToObject(root, "name", cJSON_CreateString("Jack (\"Bee\") Nimble"));cJSON_AddItemToObject(root, "format", fmt=cJSON_CreateObject());cJSON_AddStringToObject(fmt,"type",        "rect");cJSON_AddNumberToObject(fmt,"width",        1920);cJSON_AddNumberToObject(fmt,"height",        1080);cJSON_AddFalseToObject (fmt,"interlace");cJSON_AddNumberToObject(fmt,"frame rate",    24);out=cJSON_Print(root);    cJSON_Delete(root);    printf("%s\n",out);    myfree(out);    /* Print to text, Delete the cJSON, print it, release the string. *//* Our "days of the week" array: */root=cJSON_CreateStringArray(strings,7);out=cJSON_Print(root);    cJSON_Delete(root);    printf("%s\n",out);    myfree(out);/* Our matrix: */root=cJSON_CreateArray();for (i=0;i<3;i++) cJSON_AddItemToArray(root,cJSON_CreateIntArray(numbers[i],3));/*    cJSON_ReplaceItemInArray(root,1,cJSON_CreateString("Replacement")); */out=cJSON_Print(root);    cJSON_Delete(root);    printf("%s\n",out);    myfree(out);/* Our "gallery" item: */root=cJSON_CreateObject();cJSON_AddItemToObject(root, "Image", img=cJSON_CreateObject());cJSON_AddNumberToObject(img,"Width",800);cJSON_AddNumberToObject(img,"Height",600);cJSON_AddStringToObject(img,"Title","View from 15th Floor");cJSON_AddItemToObject(img, "Thumbnail", thm=cJSON_CreateObject());cJSON_AddStringToObject(thm, "Url", "http:/*www.example.com/image/481989943");cJSON_AddNumberToObject(thm,"Height",125);cJSON_AddStringToObject(thm,"Width","100");cJSON_AddItemToObject(img,"IDs", cJSON_CreateIntArray(ids,4));out=cJSON_Print(root);    cJSON_Delete(root);    printf("%s\n",out);    myfree(out);/* Our array of "records": */root=cJSON_CreateArray();for (i=0;i<2;i++){cJSON_AddItemToArray(root,fld=cJSON_CreateObject());cJSON_AddStringToObject(fld, "precision", fields[i].precision);cJSON_AddNumberToObject(fld, "Latitude", fields[i].lat);cJSON_AddNumberToObject(fld, "Longitude", fields[i].lon);cJSON_AddStringToObject(fld, "Address", fields[i].address);cJSON_AddStringToObject(fld, "City", fields[i].city);cJSON_AddStringToObject(fld, "State", fields[i].state);cJSON_AddStringToObject(fld, "Zip", fields[i].zip);cJSON_AddStringToObject(fld, "Country", fields[i].country);}/*    cJSON_ReplaceItemInObject(cJSON_GetArrayItem(root,1),"City",cJSON_CreateIntArray(ids,4)); */printf("\r\n ***mem***%d%% \r\n",mem_perused());out=cJSON_Print(root);    cJSON_Delete(root);    printf("%s\n",out);    myfree(out);printf("\r\n ***end***%d%% \r\n",mem_perused());
}

其中函数mem_perused()为获取管理内存的使用率函数。

因为之前看网上有人移植后内存出现问题，估计是没有使用正确的内存释放函数。而这里，经过上百次连续使用，内存使用没有问题。如下：

	 ***start***0% 
{"name":	"Jack (\"Bee\") Nimble","format":	{"type":	"rect","width":	1920,"height":	1080,"interlace":	false,"frame rate":	24}
}
["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"]
[[0, -1, 0], [1, 0, 0], [0, 0, 1]]
{"Image":	{"Width":	800,"Height":	600,"Title":	"View from 15th Floor","Thumbnail":	{"Url":	"http:/*www.example.com/image/481989943","Height":	125,"Width":	"100"},"IDs":	[116, 943, 234, 38793]}
}***mem***12% 
[{"precision":	"zip","Latitude":	37.766800,"Longitude":	-122.395900,"Address":	"","City":	"SAN FRANCISCO","State":	"CA","Zip":	"94107","Country":	"US"}, {"precision":	"zip","Latitude":	37.371991,"Longitude":	-122.026000,"Address":	"","City":	"SUNNYVALE","State":	"CA","Zip":	"94085","Country":	"US"}]***end***0% 

我的管理内存总共为16K，一开始使用率为0%，中间出现过使用率为12%，最后完全释放，又恢复0%。循环测试几百遍都OK。

https://blog.csdn.net/wangzibigan/article/details/85114223