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Error "Attempt to create a pointer to a constant"

 
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hemnath



Joined: 03 Oct 2012
Posts: 242
Location: chennai

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Error "Attempt to create a pointer to a constant"
PostPosted: Fri Jul 05, 2024 12:04 pm     Reply with quote
Compiler: v4.114

Error "Attempt to create a pointer to a constant".

Code:
// Function to check for "CAL" sequence
int check_CAL_sequence() {
    char buffer[4] = {0};  // Buffer to store received characters
    int index = 0;
   
    // Read characters until "CAL" sequence is detected or timeout occurs
    unsigned int16 timeout = 0;
    while (timeout < 5000) {
        if (kbhit()) {  // Check if character is available
            char received_char = fgetc();  // Read the character
           
            // Store character in buffer
            buffer[index++] = received_char;
            buffer[index] = '\0';  // Null-terminate the buffer
           
            // Check for "CAL" sequence
            if (strcmp(buffer, "CAL") == 0) {
                return 1;  // Return true if "CAL" sequence is detected
            }
           
            // Adjust buffer (shift left if buffer is full)
            if (index >= 3) {
                index = 0;  // Reset index if full (to prevent overflow)
                buffer[index] = '\0';  // Clear buffer
            }
        }
       
        delay_ms(1);  // Delay 1 millisecond
        timeout++;  // Increment timeout counter
    }
   
    return 0;  // "CAL" sequence not detected within timeout
}
Ttelmah



Joined: 11 Mar 2010
Posts: 19539

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PostPosted: Sat Jul 06, 2024 2:44 am     Reply with quote
A search here would find a lot about this.
You have a very old compiler. A method to do this was fixed in the modern
compilers. but the key is to understand the PIC, and read the manual.
In the PIC, the ROM, and RAM are two completely separate memory spaces.
So "CAL" as a constant, is stored in the ROM, and cannot be used inside
a string operation needing a RAM pointer. You can strcpy this value into
a RAM array to do the comparison.
If you read the manual section on strcmp, for your compiler, it says:
Quote:

s1 and s2 are pointers to an array of characters (or the name of an array). Note that s1 and s2 MAY NOT BE A CONSTANT (like "hi").


The note is critical.

Modern compilers can virtualise a constant like this by copying it into
a tiny temporary buffer. Uses a compiler setting 'PASS_STRINGS =
IN_RAM".

For your compiler, you have to do this yourself.
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