G-WAN C function xbuf_trunclen() and xbuf_truncptr()

Question

I would like to use the xbuf_trunclen() and xbuf_truncptr() functions to cut my buffer but the functions do not seem to work.

Here's an example with an example running via char pointer:

char *string = (char*)strdup("---Boundary");
string += 3;
printf("String is '%s'", string);

Result: String is 'Boundary'

Here is what I would like to do but does not seem to work:

xbuf_t buffer;
xbuf_init(&buffer);
xbuf_cat(&buffer, "---Boundary");
xbuf_trunclen(&buffer, 3);
printf("Buffer is '%s'", buffer.ptr);

Result: Buffer is '---Boundary'

while I would like: Buffer is 'Boundary'

and with 'xbuf_trunptr()':

...
char *ptr = (char*)strdup("Boundary");
xbuf_truncptr(&buffer, ptr);
...

Result: Buffer is '---Boundary'

while I would like: Buffer is 'Boundary'

Is this an error of use on my part or a problem of operation of the 2 functions? The goal is to manipulate the beginning of the buffer.

Answer 1

In your code, you duplicate the xbuffer's buffer so (ptr != buffer.ptr):

char *ptr = (char*)strdup("Boundary");
xbuf_truncptr(&buffer, ptr);

Doing so cannot work: ptr must belong to the [buffer.ptr, buffer.ptr + buffer.len] memory range. This would work as well: ptr[3] = 0;

And, if you merely want to cut a string with xbuf_trunclen() that's faster to do the following:

buffer.ptr[3] = 0;

Hope this helps.

Note: in restrospective, looking at these two function makes me wondering why they were created in the first place. I guess it was for Java and C# APIs and developpers (as both languages don't use C-like "strings" and encapsulate them in hidden structures).