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strcmp strange length limitation [Solved]

 
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FFT



Joined: 07 Jul 2010
Posts: 92

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strcmp strange length limitation [Solved]
PostPosted: Sun Jan 09, 2022 11:52 am     Reply with quote

Hello,

The following statement is true TEST_VAL's char length is 4 or less
Code:
if(strcmp((char *)TEST_VAL, (char *)&Buffer[1]) == 0)

true when:
Code:
#define TEST_VAL    "1234"

false when:
Code:
#define TEST_VAL    "123412341234123412341234"

Obviously Buffer[1] is start of the same string compared with the TEST_VAL.

I also tried using
Code:
#device PASS_STRINGS = IN_RAM

but nothing changed.

Buffer is defined as:
Code:
unsigned int8 Buffer[64];

and filled by serial communication.

I also tried with a custom implementation of the strcmp, result is the same.

Is this something special to CCS?

Thanks


Last edited by FFT on Mon Jan 10, 2022 8:25 am; edited 1 time in total
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sun Jan 09, 2022 12:29 pm     Reply with quote

This works:
Code:
#include <18F46K22.h>
#fuses NOWDT 
#use delay(internal=4M)
#use rs232(UART1, baud=9600, ERRORS)

#include <string.h>

unsigned int8 Test_val[64] =  "123412341234123412341234";   

unsigned int8 Buffer[64] =  "123412341234123412341234";   

//=================================
void main()
{

if(strcmp(test_val, Buffer) == 0)   
   printf("Matched\r");
else
   printf("No match\r");
   
   
while(TRUE);
     
}

I see two problems in your posted code.

Below, you are trying to create a pointer to a constant.
The compiler will give you an error. It will not compile.
Quote:
if(strcmp((char *)TEST_VAL, (char *)&Buffer[1]) == 0)


Below, you apparently think a string starts at index 1.
But it actually starts at index 0.
Quote:
if(strcmp((char *)TEST_VAL, (char *)&Buffer[1]) == 0)
FFT



Joined: 07 Jul 2010
Posts: 92

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PostPosted: Sun Jan 09, 2022 2:15 pm     Reply with quote

PCM programmer wrote:

Below, you are trying to create a pointer to a constant.
The compiler will give you an error. It will not compile.
Quote:
if(strcmp((char *)TEST_VAL, (char *)&Buffer[1]) == 0)



Thanks! This fixed my issue, v5.104 did not give an error for this. I just used a RAM variable and issue has fixed.
Ttelmah



Joined: 11 Mar 2010
Posts: 19538

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PostPosted: Mon Jan 10, 2022 1:25 am     Reply with quote

You can use the #defined version with this:
Code:

#include <18F46K22.h>
#device PASS_STRINGS=IN_RAM
#fuses NOWDT
#use delay(internal=4M)
#use rs232(UART1, baud=9600, ERRORS)
#define Test_val  "123412341234123412341234" 

#include <string.h>

unsigned int8 Buffer[64] =  "123412341234123412341234";   

//=================================
void main()
{
   if(strcmp(test_val, Buffer) == 0)   
      printf("Matched\r");
   else
      printf("No match\r");
   while(TRUE); 
}


The specific things. First understand what PCM has told you about where strings 'start'. The first byte is [0], not [1]. Then note the second line
in the code I posted. This tells the compiler to 'virtualise' constant strings
into RAM when needed.
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