STM32 - Strstr function does not work as I expected (UART)

Question

I am trying to find specific string in another string which is received via UART. However, my function returns 0, although string is not inside uart received string. Here is my function:

bool GetCommand(UART_HandleTypeDef *huart, char *command, char *getCommand, uint8_t size) {
    char *ptr;
    if (HAL_UART_Receive_IT(huart,command,size) == HAL_OK) {
        ptr = strstr(command,getCommand);
    }
    if (ptr) {
        return 1;
    } else {
        return 0;
    }
}

Program works with gcc, but it is not working as I expected when I try it with Keil. Can you help related this issue?

This seems to be the same issue: https://community.arm.com/developer/tools-software/tools/f/keil-forum/31326/strange-behaviour-strstr-function — Catsunami, Mar 24 '20 at 17:45
before using strstr make sure your string is `nul` terminated — 0___________, Mar 26 '20 at 08:14

score 2 · Answer 1 · answered Mar 25 '20 at 05:53

Your Problem is not the function strstr().

It is the way you are collecting your command

if(HAL_UART_Receive_IT(huart,command,size) == HAL_OK) {
    ptr = strstr(command,getCommand);
}

HAL_UART_Receive_IT is a non blocking function, so it returns directly after the USART is configured. This string in your command array is something undefined at this time.

Use HAL_UART_Receive() or the HAL_UART_RxCpltCallback()

score 0 · Answer 2 · edited Mar 24 '20 at 07:36

0

Try this: choose microlib in target option

look this image

edited Mar 24 '20 at 07:36

nitinkumarp

2,120
1
21
30

answered Mar 24 '20 at 01:57

Jun Zhao

3
2

Thanks for your answer. However microlib is already selected. – karamelekrobotics Mar 24 '20 at 15:37
At first，keil default complier is armcc, c lib is microlib;you can run this programmer by gcc, so i think the c lib cause this problem, maybe there is a bug in armcc c lib – Jun Zhao Mar 25 '20 at 04:06

score 0 · Accepted Answer · answered Mar 25 '20 at 22:05

Wait for the UART to complete before using memory. Do not use uninitialized variables. In addition to the other answer, you can also poll HAL_UART_State until the peripheral stops receiving.

bool GetCommand(UART_HandleTypeDef *huart, char *command, char *getCommand, uint8_t size) {
    if (HAL_UART_Receive_IT(huart,command,size) != HAL_OK) {
        // handle error
        return 0;
    }

    // wait until UART stops receiving
    while ((HAL_UART_State(huart) & HAL_UART_STATE_BUSY_RX) == HAL_UART_STATE_BUSY_RX) {
         continue;
    }

    return strstr(command, getCommand) != NULL;
}

I am grateful for your answer... It works as i planned before. Have a nice day :) — karamelekrobotics, Mar 27 '20 at 00:17

STM32 - Strstr function does not work as I expected (UART)

3 Answers3