What is the best way to reallocate memory for char array? (4 replies)

For example I've allocated memory for char *str:

str = ngx_pnalloc(r->pool, len1);

Then I've added some data to "str":

ngx_sprintf(str, "abc");

How should I reallocate this memory? Should I use:

str = ngx_pnalloc(r->pool, len2);

? And I would like to keep the str's "abc" data as well.