c - Create a pointer to two-dimensional array -

i need pointer static 2-dimensional array. how done?

static uint8_t l_matrix[10][20];  void test(){    uint8_t **matrix_ptr = l_matrix; //wrong idea  } 

i kinds of errors like:

• warning: assignment incompatible pointer type
• subscripted value neither array nor pointer
• error: invalid use of flexible array member

here wanna make pointer first element of array

uint8_t (*matrix_ptr)[20] = l_matrix; 

with typedef, looks cleaner

typedef uint8_t array_of_20_uint8_t[20]; array_of_20_uint8_t *matrix_ptr = l_matrix; 

then can enjoy life again :)

matrix_ptr[0][1] = ...; 

beware of pointer/array world in c, confusion around this.

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edit

reviewing of other answers here, because comment fields short there. multiple alternatives proposed, wasn't shown how behave. here how do

uint8_t (*matrix_ptr)[][20] = l_matrix; 

if fix error , add address-of operator & in following snippet

uint8_t (*matrix_ptr)[][20] = &l_matrix; 

then 1 creates pointer incomplete array type of elements of type array of 20 uint8_t. because pointer array of arrays, have access with

(*matrix_ptr)[0][1] = ...; 

and because it's pointer incomplete array, cannot shortcut

matrix_ptr[0][0][1] = ...; 

because indexing requires element type's size known (indexing implies addition of integer pointer, won't work incomplete types). note works in c, because t[] , t[n] compatible types. c++ not have concept of compatible types, , reject code, because t[] , t[10] different types.

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the following alternative doesn't work @ all, because element type of array, when view one-dimensional array, not uint8_t, uint8_t[20]

uint8_t *matrix_ptr = l_matrix; // fail 

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the following alternative

uint8_t (*matrix_ptr)[10][20] = &l_matrix; 

you access

(*matrix_ptr)[0][1] = ...; matrix_ptr[0][0][1] = ...; // possible 

it has benefit preserves outer dimension's size. can apply sizeof on it

sizeof (*matrix_ptr) == sizeof(uint8_t) * 10 * 20 

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there 1 other answer makes use of fact items in array contiguously stored

uint8_t *matrix_ptr = l_matrix[0]; 

now, formally allows access elements of first element of 2 dimensional array. is, following condition hold

matrix_ptr[0] = ...; // valid matrix_ptr[19] = ...; // valid  matrix_ptr[20] = ...; // undefined behavior matrix_ptr[10*20-1] = ...; // undefined behavior 

you notice works 10*20-1, if throw on alias analysis , other aggressive optimizations, compiler make assumption may break code. having said that, i've never encountered compiler fails on (but again, i've not used technique in real code), , c faq has technique contained (with warning ub'ness), , if cannot change array type, last option save :)