I am studying the Dijkstra algorithm and have not yet tried to use adjacency list. I knew I could solve the problem with an array, but the fact is that I can not get the array in the function.
If I put the code direct in main it works as expected.
This is the prototype I tried to use:
/*
* v = grafo em forma de matriz
* n = qtd de vértices
* o = origem
*/
int * Dijkstra ( int v[][], int n, int o );
In C, you need to specify the size of all dimensions of an array that is a function argument, except for the leftmost dimension size. For example, if you define that your arrays will always be 100x100, you can define the type of your function like this:
int * Dijkstra ( int v[100][100], int n, int o );
or so:
int * Dijkstra ( int v[][100], int n, int o );
The reason for this comes from the way in which matrices of C are represented in memory. Lines are placed sequentially in a vector. For example, the 3x3 array
10 20 30
40 50 60
70 80 90
It is represented in memory as a vector of size 9
M[i][j] -> 10 20 30 40 50 60 70 80 90
i -> 0 0 0 1 1 1 2 2 2
j -> 1 2 3 1 2 3 1 2 3
When you access the (i,j) field of the 3x3 array, what C does under the wads is to access the 3*i + j field of the "vector". So the compiler has to know at compile time how many columns there are in each row, which is the factor that multiplies i .
If you do not want to set the dimensions of your array at compile time there are some alternatives you can do. The most common is to use a vector of vectors rather than a multidimensional vector. So your array has a type "integer pointer vector" int ** instead of the type "two-dimensional integer vector 100x100" int [100][100] .
M -> |*| --> [10 20 30]
|*| --> [40 50 60]
|*| --> [70 80 90]
An example of how to allocate an MxN array:
// Alocando a matriz dinâmicamente
int ** mat = malloc((sizeof int*) * M;
int * buf = malloc((sizeof int) * M * N);
for(int i=0; i<M; i++){
mat[i] = &buf[N*i];
}
// Usando a matriz:
for(int i=0; i<M; i++){
for(int j=0; j<N; j++){
mat[i][j] = f(i,j);
}
}
// Libere a memória alocada dinamicamente quando você acabar de usar.
free(mat);
free(buf);