The following properties are guaranteed when storing an array:
This implies that an array is stored as a single block in memory. It is not
possible that the array is scattered in several places in the memory. In the same way
each cell precedes its next in memory. The cell
tab is stored
In the following example, we create an array of characters and display the address of each cell of the array. The display confirms that the cells of the array are consecutive: the addresses follow each other.
In computer science, there are two storage policies for multidimensional arrays:
A C compiler will always organize arrays in row-major order. Consider the following array:
Here is how the array is stored in memory:
A segmentation fault is the crash of an application that has attempted to access a memory location that was not allocated to it. Let's consider, for example, the following array:
It is an array of 10 cells, numbered from 0 to 9. What happens if you write beyond the 10th cell?
tab = 666;
The compiler detects errors only during the transformation from the source code into machine language. So writing to an element in an undeclared cell of an array is feasable. Depending on the context, here is what can happen:
A classic mistake is to write in the (N+1)th cell of an N cells array:
int tab; tab = -1; // <= Segmentation fault
Write a program that displays all the cell addresses of the 2-dimensional table below:
The expected display is the following, we can see that all the addresses follow each other:
Address of matrix: 0x7ffcab45f148 Address of matrix: 0x7ffcab45f149 Address of matrix: 0x7ffcab45f14a Address of matrix: 0x7ffcab45f14b Address of matrix: 0x7ffcab45f14c Address of matrix: 0x7ffcab45f14d Address of matrix: 0x7ffcab45f14e Address of matrix: 0x7ffcab45f14f Address of matrix: 0x7ffcab45f150 Address of matrix: 0x7ffcab45f151 Address of matrix: 0x7ffcab45f152 Address of matrix: 0x7ffcab45f153
The code below declares an array of 100 cells and displays its address (address of the first cell). Increase the size of the array until there is not enough memory to create the array. What happens?
int tab; printf ("%p\n", &tab); // &tab is equivalent to &tab, address of the first cell
We provide the declaration of the array
Write a program that asks the user for the index to be displayed. Then the program displays the cell corresponding to to the entered index. Test the program with values greater than 4.
Index of the cell to display: 4 prime = 11
Index of the cell to display: 8 prime = 4195824
Index of the cell to display: 456465461 signal: segmentation fault (core dumped)
In C, arrays are stored ...
Let's consider the following array. In memory, which cell will follow the cell
If there is not enough memory in one block to store an array, what will happen?
unsigned char image;
What is a segmentation fault?