Programming

Hi All,
Please clear the following doubt.

int main()
{
char str1[25];
char str2[] = "HelloWorld";
int len = strlen(str2);
strncpy(str1, str2, len);
str1[len] = '\0';
printf("%s", str1);
}


In the above program i'm initializing the 10th byte of str1[10] to null.
what will happen to the memory of byte 11 to 25 of str1?.

Is that memory will be used by compiler or that memory will be kept undistrubed.

Thanks in Advance,
Arun.

The contents of the memory are undefined for str1 because you did not initialize it.
After you copy "HelloWorld" and then nul terminate, then the memory after that is still undefined, ie. probably garbage. You do realize that local variables live in the user stack... and that uninitialized varables lead to bad things like buffer overflows?

One way of several to improve the code.

Also, notice I used code tags so it is easy to read:

Code:

int main()
{
   char str1[25];
   char str2[] = "HelloWorld";
   
   memset(str1,'\0',sizeof(str1));
   strncpy(str1, str2, strlen(str2));
   printf("%s\n", str1);
   return 0;
}

memset initializes str1, and main() ALWAYS returns an integer. This is very important in UNIX. Because it was initialized, str1 does need the '\0' tacked on the end. Unless you strncpy something else in there.

You don't need to blank that whole block of memory to blank the string. All you need is

Code:

str1[0]='\0';

as jim said,

its good that the variable should be given to memset,
char array blocks should be initialized.

without memset and just with a string delimiter '\0',
you end up in possible garbage retention for the char array.

There is always the potential for garbage retention in the array. The solution is to use it intelligently.

thats very much true C688...

as an user of existing libs, i dont think so programmer gets down to the stack to prevent any crash... an actual workout with memory maps and its components

And this has what to do with my example?

Like I said, there is always the potential for garbage whenever you overwrite a string of unknown contents. Should you fill all string buffers with nulls, every time you overwrite them? That could be an awful lot of nulls.