Stack Overflow Asked by Hygor Marques on December 3, 2020
I’m gonna make a program that convolves a matrix, but first I need to create this matrix and load it with random numbers, but in my methods to do this I received warnings and I cannot resolve this because I am newbie in this and this is gonna make me crazy
#include <stdio.h>
#include <stdlib.h>
#define ROW 5
#define COL 5
// Create a Matrix
int **generateMatrix(int row, int col){
int **mat;
mat=(int**)malloc(sizeof(int*)*row);
for(int i=0;i<row;i++){
mat[i]=(int*)malloc(sizeof(int)*col);
}
if(mat==NULL){
printf("Insufficient Memory...");
return 0;
}
return mat;
}
// Load a Matrix
int loadMatrix(int *x[][COL], int row, int col){
int i;
for(int r=0;r<row;r++){
for(int c=0;c<col;c++){
x[r][c]=rand()%256;
}
}
return x;
}
// Print a Matrix
void printMatrix(int *x[][COL], int row, int col){
for(int r=0;r<row;r++){
for(int c=0;c<col;c++){
printf("t%d", x[r][c]);
}
printf("n");
}
}
int main(){
int **matrix, **kernel;
// Create the Matrix
matriz=generateMatrix(ROW, COL);
kernel=generateMatrix(3,3);
// Load the Matrix
loadMatrix(matrix, ROW, COL);
loadMatrix(kernel, 3, 3);
// Print Matrix
printf("Matrixn");
printMatrix(matrix, ROW, COL);
printf("n");
printf("Kerneln");
printMatrix(kernel, 3, 3);
printf("n");
free(matrix);
free(kernel);
}
The warnings I received are bellow
main.c:25:20: warning: assignment makes pointer from integer without a cast [-Wint-conversion]
main.c:28:14: warning: return makes integer from pointer without a cast [-Wint-conversion]
main.c:35:22: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘int *’ [-Wformat=]
main.c:49:18: warning: passing argument 1 of ‘loadMatrix’ from incompatible pointer type [-Wincompatible-pointer-types]
main.c:21:9: note: expected ‘int * (*)[5]’ but argument is of type ‘int **’
main.c:50:18: warning: passing argument 1 of ‘loadMatrix’ from incompatible pointer type [-Wincompatible-pointer-types]
main.c:21:9: note: expected ‘int * (*)[5]’ but argument is of type ‘int **’
main.c:54:19: warning: passing argument 1 of ‘printMatrix’ from incompatible pointer type [-Wincompatible-pointer-types]
main.c:32:10: note: expected ‘int * (*)[5]’ but argument is of type ‘int **’
main.c:58:19: warning: passing argument 1 of ‘printMatrix’ from incompatible pointer type [-Wincompatible-pointer-types]
main.c:32:10: note: expected ‘int * (*)[5]’ but argument is of type ‘int **’
I believe you must think a bit on how do you want to build the matrix thing.
Let's say we are talking about a 5x5 array of int
int kernel[][]We will have a starting address kernel and 5 x 5 x sizeof(int) values, let's say 4 bytes to a total of 100 bytes using a 32-bits compiler. This way you would declare as int kernel[5][5]. And kernel[0] is int[5]
int** kernelWe will have kernel as a pointer to an array of pointers to int, starting at *kernel. It is another animal. kernel points to an area that has pointers to int. Let's say we have also 5 of them. kernel then points to an area of 5 pointers to int. Not an array of int. Just 5 int. In order to each one point to an array of 5 int we should have declared kernel as int* kernel[5]; and in this case *kernel[0] up to *kernel[4] would indeed point to an array of 5 int.
But note that we have no way of knowing how many pointers are in *kernel.
This is the reason why main() is declared int main(int argc, char** argv);: someone must tell the program how many pointers are in *argv.
Back to your code:
You must use this knowledge in generateMatriz() and loadMatriz().
To use array notation the last dimension must be constant. But see your prototype for loadMatriz()
int loadMatriz(int* x[][COL], int row, int col);
what is x here? It is not Plan A. It is not plan B. x is and array of pointers to int. Each element of x is a pointer to int. And it is not what you passed on main():
int main() {
int** matriz, ** kernel;
// Create the Matriz
matriz = generateMatriz(ROW, COL);
kernel = generateMatriz(3, 3);
// Load the Matriz
loadMatriz(matriz, ROW, COL);
loadMatriz(kernel, 3, 3);
kernel is int**. It is not int*[][]. Think about this. This is the reason of the compiler errors: you must build the matrix according to plan ;)
Correct answer by arfneto on December 3, 2020
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