Embedded development notes, practical knowledge sharing

Previously, in order to facilitate the testing department to save some test data , Need to temporarily develop a simple nanomsg server, With the board end client Communicate in the LAN , receive client Data and save .

As server End , You need to bind the computer IP, Different computers IP It's different , So it needs to be modified when using different computers IP To use this normally server Program .

Without recompiling the program , There are two ways to meet this need ：

• hold IP Write it in the configuration file , such as ini In the configuration file in format , then server The program reads IP, Then bind .

• server The program automatically obtains IP Address and bind .

Use these two methods respectively ：

Read from configuration file IP Address

There are many formats of configuration files , Such as JSON、INI etc. . What I choose here is INI Format of the configuration file ,.ini File is  Initialization File  Abbreviation , Initialization file .INI Document by section 、 key 、 The value of , Annotations are indicated by semicolons （;）. for example ：

  Here we use inih Parser right INI File parsing .

inih： One C language-written INI File parser .

inih The address of the parser ：

GitHub - benhoyt/inih: Simple .INI file parser in C, good for embedded systems

  meanwhile ,inih Parsers have also been included in a hodgepodge of resource summary Posts ：

EmbedSummary: Embedded hodgepodge resource summary

inih It's easy to use , Let's take a look at .

Downloaded inih The contents are shown in the figure ：

  hold  ini.c  And  ini.h  Just put it under our project . Here we use a test project ：

  meanwhile , Create a new one  ip.ini  The documents are stored in the project directory .ip.ini  The contents of the document are as follows ：

  Let's write the code test.c To parse this file ：

The analytical method is very simple （ May refer to  inih/examples  Under the demo, We also imitate this here demo To analyze ）：

• Construct a configuration structure  configuration , Define a configuration The structure is used to store the data we parse , The members in the structure are what we need to resolve INI The keys in the file . for example , our ip.ini There is... In the document ip_addr、name、num These three keys , The members in the structure represent these three keys .

• Define a handler Callback function , Used for processing parsing process . The parsing process is also very simple , matching Section Name And Key Name, Then take out the value .

• call  ini_parse  Function pair INI File parsing .

among ,handler A... Is called in the function  strdup()  The function and  atoi()  function .

• strdup() The function is c A string copying function commonly used in languages , In general, and free() Functions appear in pairs ,, because strdup() Called inside malloc() Function allocates memory for variables .

• atoi() function (ascii to integer) Is a function that converts a string to an integer .

compile 、 function ：

  Automatic access to IP Address

We can use  getifaddrs()  Function to get .getifaddrs() Function is used to obtain network card information , Include IP、 Mask 、 Broadcast address and other information .

getifaddrs() The function prototype ：

• __ifap To get the network card information .

use getifaddrs() Function to get IP The format is   The numerical format （numeric), It needs to be converted into   Expression format （presentation).inet_ntop()  Function can meet this requirement .

inet_ntop() Function is random IPv6 Functions that appear , about IPv4 Address and IPv6 All addresses apply , Function p and n Represent the   Expression format （presentation)  and   The numerical format （numeric) .IP The expression format of the address is ASCII character string , The numeric format is a binary value stored in the socket address structure . What we need here is ASCII In string form IP Address .

inet_ntop() The function prototype ：

• family Parameters ： It can be either AF_INET（ipv4） It can also be AF_INET6（ipv6）.

• addrptr Parameters ：addrptr Pointer to numeric format IP.

• strptr Parameters ：strptr Point to the expression format IP, The caller must allocate memory for the target storage unit and specify its size .

• len Parameters ： Accommodate the length of the expression format .

• Return value ： If successful, it is a pointer to the expression format , In case of error NULL.

Let's take a look at the example code ：

compile 、 function ：

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