Char pointer changes another char pointer?

Question

1.11/5 (2 votes)

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Hi all,
I have problem with my c program.

C++

//I have reduced the code (x is a counter of loop)
char *p = Path[x]; //p have the next directory in the list
if(p[strlen(p) - 1] != '\\')
{
    strcpy(p,p);
    strcat(p,"\\");
}

char *FileName = p;
strcpy(FileName,FileName);
strcat(FileName,FindFileData.cFileName);

x++;
Path[x] = FileName; // add the directory to the list

As you see above Path[] is an array of string (char*) and the first item have primary directory path (the program is scanning files in root and sub directories).
The problem is when when p changes from ("j:\d") to ("j:\d\") (in if statement) .. Path[x] changes too exactly like p???
why??

why when char pointer changes, it changes the other char pointer???

Posted 4-Feb-13 19:36pm

Rasool Ahmed

Updated 4-Feb-13 19:37pm

v2

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2 solutions

Solution 1

You're not creating a new string in your first line... you're assigning the pointer of the array Path to the character pointer p (they both point to the same memory address, I'm sure if you look at the addresses in a debugger you'll notice it's the same). If you want a new string that has the same value, you have to do a string copy (and a memory allocation for p).

Posted 4-Feb-13 20:03pm

Albert Holguin

Updated 4-Feb-13 20:04pm

v2

Comments

[no name] 5-Feb-13 5:37am

Can you show me in code.

Albert Holguin 5-Feb-13 11:31am

show you what in code? ...just google "C string copy" and I'm sure you'll get thousands of hits (if not more).

[no name] 6-Feb-13 1:55am

Alright, thanx, I will google it and if I found the solution I will posted here.

Albert Holguin 6-Feb-13 10:56am

If you have follow up questions, I'd be happy to help... but do a bit of research first.

fjdiewornncalwe 7-Feb-13 16:29pm

My 5.

Albert Holguin 7-Feb-13 17:18pm

Thanks Marcus

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H.Brydon · Accepted Answer · 2013-02-04T20:36:00

It is not clear what you are trying to do, but I think you oversimplified your code (also I believe strcpy(x, x) might be undefined behavior? or it just checks for a valid writeable buffer? or renews L1/L2/L3 cache?).

It looks like you are attempting to make sure that a directory spec has a terminating '\' character, then you append a filename to the directory spec. The 2 strcpy() calls don't do anything valid with the code as you present here. The strcat() calls do the heavy lifting for the 2 append operations. The 2 pointers 'p' and 'Filename' are pointers within the 'Path' buffer. If you append something to the end of either 'p' or 'Filename' you also append to 'Path'. They are all pointing within the same buffer space.