Adjacency matrix of graph in c ( getting error ) - c

Question

#include <stdio.h>
struct graph{
int v,e,**adj;
};
struct graph* graph_A(){
int u,V,i;
struct graph *g = (struct graph*)malloc(sizeof(struct graph));
if(!g){
printf("error ! ");
exit(1);
}
printf("Enter no of nodes and edges ? ");
scanf("%d, %d",&g->v,&g->e);
g->adj = (int**)malloc(sizeof(int) * sizeof(g->v * g->v ));
for(u = 0 ; u <= g->v ; u++)
for(V = 0 ; V <= g->v ; V++ )
g->adj[u][V] = 0;
printf("Enter connections ? ");
for(i = 0 ; i <= g->e ; i++){
scanf("%d, %d",&u,&V);
g->adj[u][V] = 1;
g->adj[V][u] = 1;
}
return (g);
}
int main(){
graph_A();
}
I am trying to figure out whats the problem but unable to resolve by myself . please help !
i've researched for about 2 hours over this topic unfortunately did't found any
proper help desk.
i am learning data structure and implementing in c and c++ language.
if you could able to advice me
that'd be earnestly kind of you .
thanks !

Answer 1

Slightly fixed your code using vectors. Not the cleaniest way due to non-use of auto loops, bad choices of variables, no boundary check on user input, but at least it works
I have removed the allocations fully, replaced by vectors, much simpler, and the fact is that the code did not change that much.
Note that you don't need a graph class. Everything could have been done in the main itself. If you want to create a class, then provide parameters in the constructor instead of interactive input (do that in the main so others can reuse your class for other purposes), and provide methods to compute, get access to data, size, etc... That will come afterwards.
Which were the main concerns:
malloc of the instance within the constructor itself. Using new would have created an infinite recursion. My advice: read some C++ books
all loops include upper boundary
the pointer of pointer row was allocated but not the rows themselves.
When I rewrote the code, I had 2 compilation errors, one SEGV because of the last upper bound boundary error on the display part, after that it worked right away. C++ rules (when you know your way around)
code:
#include <iostream>
#include <cstdlib>
#include <vector>
using namespace std;
class graph{
int v,e;
vector<vector<int> > adj;
public:
graph();
};
graph::graph()
{
int u,V,i;
cout << "Enter no of nodes and edges ? ";
cin >> v ;
cin >> e ;
adj.resize(v);
for(u = 0 ; u < v ; u++)
{
adj[u].resize(v);
}
for(u = 0 ; u < v ; u++)
for(V = 0 ; V < v ; V++ )
adj[u][V] = 0;
cout << " Enter connections ? ";
for(i = 0 ; i < e ; i++){
cin >> u ;
cin >> V ;
adj[u][V] = 1;
adj[V][u] = 1;
}
for(u = 0 ; u < v ; u++)
{
for(V = 0 ; V < v ; V++ )
{
cout << adj[u][V] << " ";
}
cout << endl;
}
}
int main(){
graph a;
return 0;
}
test:
Enter no of nodes and edges ? 10 3
Enter connections ? 3 4
2 3
4 5
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 1 0 0 0 0 0 0
0 0 1 0 1 0 0 0 0 0
0 0 0 1 0 1 0 0 0 0
0 0 0 0 1 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0