[SOLVED] Mystery segfault

[lemons]

Hi guys,

I really am out of my depth here, unless I'm missing something that's screaming at me!

I have a C method which trims any leading zeroes off a number in char* form:

    33   void myTrim(char* number)
    34   {
    35      assert(number);
    36      
    37      if (number[0] == 48)
    38      {
    39         uint64 i = 0;
    40         uint64 j;
    41         
    42         uint64 numberLength = strlen(number);
    43         
    44         while (number[i] == 48)
    45         {
    46            i++;
    47         
    48            if (i == numberLength)
    49            {
    50               /*
    51                  SPECIAL CASE: all digits are zero, i.e., number is zero
    52                  (regardless of zero padding!)
    53               */
    54            
    55               number[0] = 48; // '0'
    56            
    57               for (j = 1; j < numberLength; j++)
    58                  number[j] = 0; // '\0'
    59               
    60               return;
    61            }
    62         }
    63      
    64         uint64 size = numberLength - i;
    65      
    66         for (j = 0; j < size; j++)
    67            number[j] = number[j + i];
    68      
    69         for (; j < numberLength; j++)
    70            number[j] = 0;
    71      }
    72   }

uint64 is typedef'd as unsigned long long in this case and is compiled and ran on x86_64. The segfault occurs at line 67. I pass the string "0102" into the method and it happens!

Using GDB at that line after the segfault, I can see that:

(gdb) print i
$1 = 1
(gdb) print j
$2 = 0
(gdb) print number
$3 = 0x4012d9 "0102"

number is pointing to the same address as when the method was entered, and even more 'bafflingly':

(gdb) print number[j]
$5 = 48 '0'
(gdb) print number[j + i]
$6 = 49 '1'

I can get GDB to execute the line with no problems.

So, as far as I can tell, the line being executed at the segfault is

number[0] = number[0 + 1]

and both array indices are legal and fine?

Why is this happening? Any help will be much appreciated!

Thanks

[lemons]

Sorry, I've solved it now. The number was initialised as

char* number = "0102";

which wasn't right.

Apologies!