Segmentation fault

Hi all,

I've got a segmentation fault occurring that I don't understand, and I'd appreciate your help. First, the relevant structure

Code:

typedef struct node
{
	//sequence for this node
	amino_acid_list *sequence;

	// not currently used- in case sequence length changes
	int sequence_length;
	
	// distance (in amino acid substitutions) 
	int mutation_distance_from_parent;
	int mutation_distance_to_left;
	int mutation_distance_to_right;

	// distance (absolute? not yet used)
	int distance_from_parent;
	int distance_to_left;
	int distance_to_right;
	
	// depth of this node
	int depth;
	
	// debugging
	long int data;
	
	// pointers
	struct node *parent_ptr;
	struct node *left_ptr;
	struct node *right_ptr;
} node

Here is the function definition

Code:

node *build_tree_with_constraints(node *n, node* nprev, int depth, int maxdepth, amino_acid_list *parent_sequence, int sequence_length, float ........r, float **tpm, int dist, float random_param_one, float random_param_two, int burnin, incompatability_matrix **icm, int num_amino_acids, int type, int *num_mutations);

And here is the offending piece of code within the function build_tree_with_constraints

Code:

			n->left_ptr= build_tree_with_constraints(n->left_ptr, n, n->depth+1, maxdepth, n->sequence, sequence_length, ssr, tpm, dist, random_param_one, random_param_two, burnin, icm, num_amino_acids, type, num_mutations);

                        // make sure that we get the correct output here
			printf("LEFT- number of mutations is %d\n", *num_mutations);

			// set the distance to the left offspring node
			n->mutation_distance_to_left= *num_mutations;
			printf("one\n");
			n->left_ptr->mutation_distance_from_parent= *num_mutations;
			printf("two\n");

Here is the output

Code:

number of mutations is 48
LEFT- number of mutations is 48
uno
Segmentation fault

I don't understand why

Code:

n->mutation_distance_to_left= *num_mutations;

works, but

Code:

n->left_ptr->mutation_distance_from_parent= *num_mutations;

Doesn't. I've also tried

Code:

(n->left_ptr)->mutation_distance_from_parent= *num_mutations;

But that doesn't help either. So obviously I'm missing something fairly basic, but I don't know what it is.

Thanks a lot,
Brad

Run the code in a debugger. When the segfault occurs the debugger will stop. Investigate the state of the program at the point of the failure.

Try this:
RMS's gdb Tutorial