5添加评论分享收藏感谢收起赞同 添加评论分享收藏感谢收起json在arduino上的应用_Arduino入门与进阶
json在arduino上的应用
作者：duino123.com
json在arduino上的应用
This library is primarily design to be used with the Arduino IDE and therefore has a simplified setup procedure for that environment. If you don't use the Arduino IDE, please read&.
Install the library
For Arduino 1.6.x and above
ArduinoJson is available in Arduino's Library Manager. You can automatically install it from there.
Note: if ArduinoJson doesn't appear in Libray Manager, or if only old versions are listed, try to delete the local cache. For example, on Windows, you need to delete:
%LOCALAPPDATA%\Arduino15\library_index.json
%LOCALAPPDATA%\Arduino15\library_index.json.tmp.gz
You don't even need to close Arduino, just re-open the library manager.
For older Arduino IDE
You needed to&&and extract it to:
&your Arduino Sketch folder&/libraries/ArduinoJson
Then restart the Arduino IDE.
NOTE: There are two packages the standard and the &old-layout&. You need to use the &old-layout& for Arduino 1.0.X, Energia and other alternative IDE.
For Visual Micro / Visual Studio 2015 / Atmel Studio
You need the latest version (January 2016 or later) of&&installed for Visual Studio or Atmel Studio.
Run the examples sketches
Click&File&/&Example&/&ArduinoJson.
Use the library in your sketches
Just add the following line at the top of your program:
#include &ArduinoJson.h&
Then follow the instructions:
This page contains a detailed guide on how to parse a JSON string using the Arduino JSON library
Before writing any code, don't forget to include the header:
#include &ArduinoJson.h&
For instructions on how to install the library, please read&&or&.
Here an example that parse the string&{&sensor&:&gps&,&time&:,&data&:[48..302038]}:
char json[] = &{\&sensor\&:\&gps\&,\&time\&:,\&data\&:[48..302038]}&;
// Step 1: Reserve memory space
StaticJsonBuffer&200& jsonB
// Step 2: Deserialize the JSON string
JsonObject& root = jsonBuffer.parseObject(json);
if (!root.success())
Serial.println(&parseObject() failed&);
// Step 3: Retrieve the values
const char* sensor
= root[&sensor&];
= root[&time&];
= root[&data&][0];
longitude = root[&data&][1];
Step 1: Reserve memory space
Arduino JSON uses a preallocated memory pool to store the object tree, this is done by theStaticJsonBuffer.
Before continuing please read the page&&that explains everything you need to know about&StaticJsonBuffer.
Step 2: Parse the JSON string
You invoke the JSON parser through the instance of&StaticJsonBuffer. It exposes two functions for parsing JSON:
parseArray()&that returns a reference to a&JsonArray
parseObject()&that returns a reference to a&JsonObject
Let's see an example. Say we want to parse&{&sensor&:&gps&,&time&:,&data&:[48..302038]}, it's an object so we call&parseObject()&as follows:
char json[] = &{\&sensor\&:\&gps\&,\&time\&:,\&data\&:[48..302038]}&;
JsonObject& root = jsonBuffer.parseObject(json);
As you can see&parseObject()&takes a&char*&as a parameter. Be careful, it's not a&const char*, the memory must be writable. Indeed, the parser will modify the string in two cases:
to insert string endings (character&\0),
to translate escaped characters (like&\n&or&\t).
Another thing that you must keep in mind is that the string (char json[]&in the example above) must stay in memory during the whole parsing process. That is because the in memory object tree will store pointer to chunks of the string, so as to avoid any memory duplication.
Now, to check if the parsing was successful, you can call&JsonObject::success():
if (!root.success())
// Parsing fail
The result can be&false&for three reasons:
the JSON string is invalid,
the JSON string doesn't represent an object,
the&StaticJsonBuffer&is too small.
We just saw how to parse an object, there is nothing more to say for arrays, the procedure is exactly the same.
Step 3: Retrieve the values
Now that the object or array is in memory, you can extract the data very easily.
In this section, we'll see how to do it with a&JsonObject. Once again, there is nothing more to say about arrays,&JsonArray&works exactly the same as&JsonObject.
Subscript operator
The simplest way is to use the subscript operator of&JsonObject:
const char* sensor = root[&sensor&];
long time = root[&time&];
You can chain the subscript operator if you have nested arrays or objects:
double latitude
= root[&data&][0];
double longitude = root[&data&][1];
But alternatively, you can get a reference to the nested array:
JsonArray& nestedArray = root[&data&];
Casting values
In the previous examples, the values were implicitly casted to the target type. You can also do this explicitly
const char* sensor = root[&sensor&].asString();
long time = root[&time&].as&long&();
JsonArray& nestedArray = root[&data&].asArray();
If the actual value doesn't match the target type, a default value will be return:
false&for boolean values
0&for integer values
NULL&for string values
JsonArray::invalid()&for nested arrays
JsonObject::invalid()&for nested object
Check values
If you want to know if some value is present, call&containsKey():
if (root.containsKey(&extra&))
// root[&extra&] is valid
If you want to check the type value has a certain type, call&is&T&():
if (root[&extra&].is&JsonArray&&())
// root[&extra&] is an array
You can also iterate through the key-value pairs of the object:
for (JsonObject::iterator it=root.begin(); it!=root.end(); ++it)
Serial.println(it-&key);
Serial.println(it-&value.asString());
Advanced Example
Let's take what we've learned above up a gear :)
Our JSON array is now:
char json[] = &{\&data\&:{\&time\&:{\&day\&:1,\&month\&:3,\&year\&:16,\&hours\&:9,\&mins\&:59,\&secs\&:14}}}&;
We parse it and check it as before with:
JsonObject& root = jsonBuffer.parseObject(json);
// Test if parsing succeeds.
if (!root.success()) {
Serial.println(&parseObject() failed&);
Now to get the data, we can follow the object downwards, just like you would do with PHP etc...:
= root[&data&][&time&][&day&];
= root[&data&][&time&][&month&];
= root[&data&][&time&][&year&];
= root[&data&][&time&][&hours&];
= root[&data&][&time&][&mins&];
= root[&data&][&time&][&secs&];
This allows for more complex data to be processed, the time as in this example or numerous values from a single function. Just make sure your jsonBuffer is large enough to handle the larger objects!
See the file called &JsonParserExample_Advanced.ino& in &ArduinoJson/examples/JsonParserExample/&
This page contains a detailed guide on how to generate a JSON string using the Arduino JSON library
Before writing any code, don't forget to include the header:
#include &ArduinoJson.h&
For instructions on how to install the library, please read&&or&.
Here is an example to generate&{&sensor&:&gps&,&time&:,&data&:[48..302038]}
// Step 1: Reserve memory space
StaticJsonBuffer&200& jsonB
// Step 2: Build object tree in memory
JsonObject& root = jsonBuffer.createObject();
root[&sensor&] = &gps&;
root[&time&] = ;
JsonArray& data = root.createNestedArray(&data&);
data.add(48.756080, 6);
// 6 is the number of decimals to print
data.add(2.302038, 6);
// if not specified, 2 digits are printed
// Step 3: Generate the JSON string
root.printTo(Serial);
Step 1: Reserve memory space
Arduino JSON uses a preallocated memory pool to s this is done by theStaticJsonBuffer.
In the case of a&StaticJsonBuffer, the memory is reserved on the stack. The template parameter (200&in the example) is the number of bytes to reserved.
Alternatively, you can use a&DynamicJsonBuffer&that allocates memory on the heap and grow as required. It is the preferred way for devices with a significant amount of RAM, like the ESP8266.
Step 2: Build object tree in memory
Once the&JsonBuffer&is ready, you can use it to build your in-memory representation of the JSON string.
You create an array like this:
JsonArray& array = jsonBuffer.createArray();
Don't forget the&&&after&JsonArray; it needs to be a reference to the array.
Then you can add strings, integer, booleans, etc:
array.add(&bazinga!&);
array.add(42);
array.add(true);
There are 3 syntaxes for floating point values:
array.add(3.1415);
// default:
2 digits -& &3.14&
array.add(double_with_n_digits(3.1415, 4));
// explicit: 4 digits -& &3.1415&
array.add(3.1415, 4);
// same as previous
-& &3.1415&
About floating point precision
The overload of&add()&with 2 parameters allows you to specify the number of decimals to save in the JSON string. When you use the overload with one parameter, you use the default number of decimals which is 2. Note that this behavior is the same as Arduino'sPrint::print(double,int)&which is implemented by&Serial, so you may already be familiar with this behavior.
You can add a nested array or object if you have a reference to it. Or simpler, you can create nested array or nested objects from the array:
JsonArray&
nestedArray
= array.createNestedArray();
JsonObject& nestedObject = array.createNestedObject();
You create an object like this:
JsonObject& object = jsonBuffer.createObject();
Again, don't forget the&&&after&JsonObject, it needs to be a reference to the object.
Then you can add strings, integer, booleans, etc:
object[&key1&] = &bazinga!&;
object[&key2&] = 42;
object[&key3&] = true;
As for the arrays, there are two syntaxes for the floating point values:
object[&key4&] = double_with_n_digits(3.1415, 4);
// 4 digits &3.1415&
object[&key5&] = 3.1415;
// default: 2 digits &3.14&
You can add a nested array or object if you have a reference to it. Or simpler, you can create nested array or nested objects from the object:
JsonArray&
nestedArray
= object.createNestedArray(&key6&);
JsonObject& nestedObject = object.createNestedObject(&key7&);
Other JsonObject functions
object.set(key, value)&is a synonym for&object[key] = value
object.set(key, value, digits)&is a synonym for&object[key] = double_with_n_digits(value, digits)
object.containsKey(key)&returns&true&is the&key&is present in&object
object.remove(key)&removes the&value&associated with&key
Step 3: Generate the JSON string
There are two ways tho get the resulting JSON string.
Depending on your project, you may need to dump the string in a classic&char[]&or send it to aPrint&implementation like&Serial&or&EthernetClient.
Both ways are the easy way :-)
Use a classic&char[]
Whether you have a&JsonArray&&or a&JsonObject&, simply call&printTo()&with the destination buffer, like so:
char buffer[256];
array.printTo(buffer, sizeof(buffer));
Want an indented output?
By default the generated JSON is as small as possible. It contains no extra space, nor line break. But if you want an indented, more readable output, you can. Simply call&prettyPrintTo&instead of&printTo():
array.prettyPrintTo(buffer, sizeof(buffer));
Send to a&Print&implementation
It is very likely that the generated JSON ends up in a stream like&Serial&or&EthernetClient, so you can save some time and memory by doing this:
array.printTo(Serial);
And, of course if you need an indented JSON string:
array.prettyPrintTo(Serial);
About the Print interface
The library is designed to send the JSON string to an implementation of the&Print&interface that is part of Arduino. In the example above we used&Serial, but they are many other implementations that would work as well, including:&HardwareSerial,&SoftwareSerial,LiquidCrystal,&EthernetClient,&WiFiClient,&Wire... When you use this library out of the Arduino environment, it uses its own implementation of&Print&and everything is the same.
Length of the output data
If you need to know the length of the output data beforehand, use the&measureLength()&method:
int len = array.measureLength();
That comes in handy when you need to calculate the&Content-Length&when posting JSON data over HTTP.
内容来源：https://codeload.github.com/rengaoadmin/ArduinoJson/zip/master&
如需更详细资料，如有好资源分享，请加入QQ交流群：
欢迎阅读，欢迎转载，不用注明出处！本站只提供入门和进阶资料，做您学习的小伙伴！请加群：
两块Arduino之间通过SPI通信
常见的几种arduino型号的IIC引脚定义
Arduino软串口的使用
[]Arduino串口从基础到高级最全面教程
自动化世界3823 条评论分享收藏感谢收起赞同 2325 条评论分享收藏感谢收起Arduino IDE for ESP8266快速入门教程 | 风之工房
最受欢迎的文章
- 2,651 阅读 - 33,522 阅读 - 11,452 阅读 - 9,780 阅读 - 7,881 阅读 - 7,497 阅读
Theme | Powered by【arduino】for循环输出问题求解_arduino吧_百度贴吧
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&签到排名：今日本吧第个签到，本吧因你更精彩，明天继续来努力！
本吧签到人数：0成为超级会员，使用一键签到本月漏签0次！成为超级会员，赠送8张补签卡连续签到：天&&累计签到：天超级会员单次开通12个月以上，赠送连续签到卡3张
关注：56,448贴子：
【arduino】for循环输出问题求解收藏
arduino, 750多家厂商代理,100多万种现货库存,当天出货,免费送货.
图可能看不太清，我描述一下我设计一个写字机器人，将他的作图范围分为50x120的坐标系，以左下角第一个点为原点，想自（30，20）至（30，120）做条线段，用for 循环编的程序，每次输出都+1，到120停止。他程序出来大概应该是2252202252212253222252但是他输出的确实2252200210220或着2252202252212253221488之后开始加1然显示一个四位数这是为什么。。。
不贴代码大罗神仙都没辙……
登录百度帐号}