int igraph_strvector_resize(igraph_strvector_t* v, long int newsize);

If the new size is bigger then empty strings are added, if it is smaller then the unneeded elements are removed.

Arguments: 

Returns: 

Time complexity: O(n), the number of strings if the vector is made bigger, O(l), the total length of the deleted strings if it is made smaller, maybe less, depending on memory management.