STM32F411RET6 - Working with pointers

[hackerli90]

Posted on September 16, 2015 at 15:48

Hello

Im working on a simple uController software to control a clock. Im working with a Nucleo controllerboard (STM32F411RET6) and uVision Keil V5.To be able to manipulate acutal variables instead of copies, id like to work with pointers (and as far as i know, char array need to be handled as pointers anyway). I placed my questions 1-11 directly at the line where i dont know how to work with those values. thanks for advise.Software:// main.h prototypes:void time_clock_management(int* ss, int* mm, int* hh);    // declare as pointers correct? Question 1void USART_string_send(char* text);                       // declare as pointer correct? Question 2// main.c private variables:char TxOptions[] = ''\n\rOptions:\n\r\ts set time\n\r''; //!uint8_t sec = 0;uint8_t min = 0;uint8_t hour = 0;// main.c functions:void time_clock_management(int* ss, int* mm, int* hh){    // declare as pointer correct? Question 3 /* Count */ *ss++;                                                  // work with variable (acutal value, pointer) instead of adress correct? Question 4 if(*ss==60){*ss=0; *mm++;}                              // work with variable (acutal value, pointer) instead of adress correct? Warning: expression result unused. Question 5 if(*mm==60){*mm=0; *hh++;}                              // work with variable (acutal value, pointer) instead of adress correct? Warning: expression result unused. Question 6  if(*hh==13){*hh=1;}                                     // work with variable (acutal value, pointer) instead of adress correct? Question 7}void USART_string_send(char* text){                       // declare as pointer correct? Question 8 foo_func_where_param_charArr_is_required(*text);        // place as pointer into a function? Question 9}// main.c call functions:time_clock_management(&sec, &min, &hour);                 // here *pointer, &reference or actual value?? Question 10USART_string_send(TxOptions);                             // here *pointer, &reference or actual value?? Question 11 #pointers

[qwer.asdf]

Posted on September 16, 2015 at 16:12

Question 1:

No, your sec, min and hour variables are uint8_t type, so the pointers must also be uint8_t*, so the correct way is: void time_clock_management(uint8_t* ss, uint8_t* mm, uint8_t* hh); Question 2: Yes Question 3: See Question 1 Question 4: Yes Question 5: Yes Question 6: Yes Question 7: Yes Question 8: Yes Question 9: where is foo_func_where_param_charArr_is_required definition? You are passing one char to it (the first character of the string). Maybe you wanted to pass the string, then foo_func_where_param_charArr_is_required(text); is the correct way of doing it. Question 10, Question 11: There are no references in C (you are using C not C++ right?) time_clock_management(&sec, &min, &hour); // It's OK, you are passing pointers which are being expected USART_string_send(TxOptions); // Also OK, you passing pointer which is expected by the function You should read books on C, or some online tutorials at least, like http://pw1.netcom.com/~tjensen/ptr/pointers.htm (first thing in google)

[Tesla DeLorean]

Posted on September 16, 2015 at 17:17

Not sure that's right,

*ss++;  // Advances the pointer, reads the value to nowhere (*ss)++; // Increments the value pointed too, not the pointer These would be equivalent USART_string_send(TxOptions); USART_string_send(&TxOptions[0]);

[Tesla DeLorean]

Posted on September 16, 2015 at 17:20

The logic you're looking for

void time_clock_management(uint8_t* ss, uint8_t* mm, uint8_t* hh); // Proto type     void time_clock_management(uint8_t* ss, uint8_t* mm, uint8_t* hh)

{ /* Count */ (*ss)++; if(*ss==60){*ss=0; (*mm)++;} if(*mm==60){*mm=0; (*hh)++;} if(*hh==13){*hh=1;} }