Thread: Superfluous characters after string -- pointer issues?

Instead of repeatedly using strlen to obtain the length of a string whose length does not change, it would be more efficient and readable to cache the string length. This would also allow you to use strcpy instead of strcat to copy to the point in dest that has not yet been written to, thereby skipping over the effort strcat has to go through to find the null character.

> How can this not leak memory?
Because it isn't a call to malloc.

Well it might be a call to malloc, but it would be one the compiler generates, and it would be the compiler that would be responsible for calling free.

> The thing is, the one time I'm actually using the "n" functionality is with the first strncpy
You still need to take care of appending the \0 in the correct place then.

Your destination array starts out containing garbage, so you need to make sure you always have a valid string (with it's \0) when you're building up your new string.

Originally Posted by CommonTater

I dunno... I'll have to write a test proggy and look at it in the debugger... but it seems to me that creating a runtime static array then creating a second one with the same name probably is creating orphaned blocks on the stack... It will be interesting to investigate.

If your investigation shows that that happens then you have a real live compiler bug to report

Originally Posted by C99 Clause 6.2.4 Paragraph 2 (part)

The lifetime of an object is the portion of program execution during which storage is guaranteed to be reserved for it. An object exists, has a constant address, and retains its last-stored value throughout its lifetime.

Originally Posted by C99 Clause 6.2.4 Paragraph 4

An object whose identifier is declared with no linkage and without the storage-class specifier static has automatic storage duration.

Originally Posted by C99 Clause 6.2.4 Paragraph 5 (part)

For such an object that does not have a variable length array type, its lifetime extends from entry into the block with which it is associated until execution of that block ends in any way.

Originally Posted by C99 Clause 6.2.4 Paragraph 6

For such an object that does have a variable length array type, its lifetime extends from the declaration of the object until execution of the program leaves the scope of the declaration. (Note 27) If the scope is entered recursively, a new instance of the object is created each time. The initial value of the object is indeterminate.

Originally Posted by C99 Clause 6.2.4 Note 27

Leaving the innermost block containing the declaration, or jumping to a point in that block or an embedded block prior to the declaration, leaves the scope of the declaration.

Originally Posted by CommonTater

However; all doubt would be removed with a call to malloc in that spot instead of creating an array on the stack...

Not all doubt: you still need to check for a corresponding call to free (or otherwise). Also, it seems to me that variable length arrays are not required to be created on the stack.