scanf() can only read one character

[LittleYe233]

I am trying to use scanf() in STM32H743, referring a webpage (here). More specifically, after setting up USART1 in STM32CubeMX, I add some function prototypes like:

#ifdef __GNUC__
#define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
#define GETCHAR_PROTOTYPE int __io_getchar(void)
#else
#define PUTCHAR_PROTOTYPE int fputc(int ch, FILE *f)
#define GETCHAR_PROTOTYPE int fgetc(FILE *f)
#endif

PUTCHAR_PROTOTYPE
{
  HAL_UART_Transmit(&huart1, (uint8_t *)&ch, 1, HAL_MAX_DELAY);
  return ch;
}

GETCHAR_PROTOTYPE
{
  uint8_t ch = 0;

  /* Clear the Overrun flag just before receiving the first character */
  __HAL_UART_CLEAR_OREFLAG(&huart1);

  /* Wait for reception of a character on the USART RX line and echo this
   * character on console */
  HAL_UART_Receive(&huart1, (uint8_t *)&ch, 1, HAL_MAX_DELAY);
  // HAL_UART_Transmit(&huart1, (uint8_t *)&ch, 1, HAL_MAX_DELAY);
  return ch;
}

and add a scanf() in the main function before infinite while loop:

scanf("%c", &c);

where c is a char.

I found that if I read one character (e.g. a char variable) every time, the function works well. But if I try to read more like integers and strings, the function seems being stuck. I don't know where it is stuck and why it happened. Please help. Any help is appreciated.

EDIT: I have added "setvbuf(stdin, NULL, _IONBF, 0);" before any scanf() call.

[Peter BENSCH]

Try deactivating the buffering before scanf():

setvbuf(stdin, NULL, _IONBF, 0);

Regards
/Peter

[SMarie]

Did you add the config indicated in the link you gave ?

setvbuf(stdin, NULL, _IONBF, 0);

If not could you try it ?
If you did, could you show us the rest of your code ?

S. Marie

[Andrew Neil]

---

@LittleYe233 wrote:

But if I try to read more like integers and strings, the function seems being stuck.

---

How, exactly, are you testing that?

@Peter BENSCH and @SMarie have suggested disabling buffering - so does your input work as-is if you terminate entry with CR and/or LF ?

EDIT:

See this thread on the buffering of stdin, etc:

https://community.st.com/t5/stm32-mcus-products/stm32g030-usart-and-hal-delay-strange-behavior/m-p/640684

[LittleYe233 · Accepted solution]

@Peter BENSCH @SMarie @Andrew Neil Thanks for your fast replies. I forget to mention in the first thread that I actually added "setvbuf()" before any scanf() call. And I found that this situation happened because I forgot to automatically add LF after my input in the serial termial. With LF or CR/LF, scanf() begins to work well again. That's all my fault and thank you all again.

[Andrew Neil]

Good to hear - please mark the solution:

https://community.st.com/t5/community-guidelines/help-others-to-solve-their-issues/ta-p/575256

I think this is defined behaviour for stdin in the standard C library.