Definition and usage of several special standards of C language

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author | strongerHuang

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C Language has many special uses , If these special uses are used properly , Your code will become more robust , Easier to maintain .

For example, we are using STM32 Library assertion （assert）, You will find that the official offer contains “__FILE__、__LINE__” Code for .

The standard peripheral library is located in stm32fxxx_conf.h file ：

#define assert_param(expr) ((expr) ? (void)0 : assert_failed((uint8_t *)__FILE__, __LINE__))

HAL Can make Assert：

In the code, you will see the following code ：

If you add this assertion code , For developing large 、 Complex system , This sentence is actually very useful . Every time the program runs incorrectly , It will print the location specified by the program code , It is convenient for us to quickly find the wrong location in the huge program .

Our system will over time , Constantly update , That is, you need to submit many versions of executable files （hex、bin etc. ）. however , The product is in later use , We upgraded some devices , Some devices may be ignored （ Forget to upgrade ）, If there is a fault , How can we quickly find out which version of the software has failed ？

Our system will over time , Constantly update , That is, you need to submit many versions of executable files （hex、bin etc. ）. however , The product is in later use , We upgraded some devices , Some devices may be ignored （ Forget to upgrade ）, If there is a fault , How can we quickly find out which version of the software has failed ？

C Several special standard definitions

__FILE__ ： Compiling file name

__LINE__ ： Compiling line number of file

__DATE__： Date string at compile time Such as “Sep 22 2020”

__TIME__： Time string at compile time   Such as ”10:00:00“

__STDC__： Judge whether the document is the standard C Program

1.__FILE__ Compile file name

File Chinese means document , The meaning here mainly refers to ： The file being compiled corresponds to the path of the file being compiled and the name of the file .

Keil The path corresponding to the version is the path relative to the project file ,IAR The version path is relative Windows route .

Source code ：

char BuildFile[] = __FILE__;
printf(" Compile file path ：%s\n", BuildFile);

Keil：

Compile file path ：App\main.c

IAR：

Compile file path ：C:\Users\strongerHuang\Desktop\ Project master directory \App\main.c

2.__LINE__ Compile file line number

The above is the compiled file name , Is a string , And here is the line number , It's an integer variable , This is the difference between the two ,

For example, add source code to the project ：

char BuildLine = __LINE__;
printf(" The line where the code was compiled ：%d\n", BuildLine);

You can see strings that are not arrays , Print information ：

The line where the code was compiled ：44

In general ,__FILE__ Is and __LINE__ Use together , Used to print our code information , Convenient and fast location of code .

3.__DATE__ Compile date

__DATE__ date , It should be noted that ： This date is when you compile Windows The date of the system , If the corresponding part of the code has been compiled before , There is no compilation later , This date is still the previous date , Instead of the later compilation date . therefore , If this is used to finalize the version , You need to recompile the project completely when finalizing the version , It will be updated to the date of your last compilation .

Code ：

char BuildDate[] = __DATE__;
printf(" Compile date ：%s\n", BuildDate);

Output results ：

Compile date ：Sep 22 2017

4.__TIME__ Compile time

This and __DATE__ The same principle , Compile time , Also a string .

Once again remind ： Used to finalize the version ： Recompile required , This is the last compilation time .

Code ：

char BuildTime[] = __TIME__;
printf(" Compile time ：%s\n", BuildTime);

Output results

Compile time ：10:00:00

5.__STDC__ standard C Code

This standard is rarely used in our MCU and embedded programming , When the procedure is required to be strictly followed ANSIC The identifier is assigned as 1, It is mainly to judge whether our procedure documents are standards C Program .

Code ：

#ifdef __STDC__
  printf(" standard C Code file \n");
#else
  printf(" Nonstandard C Code file \n");
#endif

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