“excess elements in scalar initializer” when using igraph C library to generate a network with power law degree distribution

Question

I'm using igraph C library and I want to generate a undirected, without loop, and a single edge network with power law degree distribution. The parameters I have are:

• number of nodes = 25,000
• number of edges = 25,000
• alpha = 2.16104

I want to use the igraph_static_power_law_game graph generator and I wrote the following code.

#include <igraph.h>

int main() {

  igraph_t g;
  int igraph_static_power_law_game(&g, 25000, 25000, 2.16104, -1, 0, 0, 1);
  igraph_destroy(&g);

  return 0;
}

I use the the following command to compile the code.

gcc testpw.cpp -I/usr/local/Cellar/igraph/0.7.1/include/igraph -L/usr/local/Cellar/igraph/0.7.1/lib -ligraph -o testpw

And the following error appeared.

error: excess elements in scalar initializer
  int igraph_static_power_law_game(&g, 25000, 25000, 2.16104, -1, 0, 0, 1);
      ^                              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

Since I can't find an example of using igraph C library to generate power-law degree network online, I don't know what's the way to make it. Am I doing something wrong here?

Answer 1

If you're compiling C code, you don't need the int before igraph_static_power_law_game() , because that makes the line look like a faulty declaration of the function instead of an invocation of the function.

Or, if you're compiling C++ code, the compiler is interpreting the contents of the parentheses as an initializer for the variable igraph_static_power_law_game and complaining that a single int variable does not need multiple initializers.

Either way, writing:

igraph_static_power_law_game(&g, 25000, 25000, 2.16104, -1, 0, 0, 1);

fixes the immediate compilation error. You should probably be using something like:

if (igraph_static_power_law_game(&g, 25000, 25000, 2.16104, -1, 0, 0, 1) != 0)
    …report error…

so that if the function fails, you know about it.