Create 2D array from existing 1D arrays in C? -

in perl can create 1d arrays , create 2d array them, following way:

@a1=(a,b,c) @a2=(d,e,f) @a3=(g,h,i) @m23_v1=(\@a1,\@a2,\@a3) 

here way (assuming @a1, @a2 , @a3 same in previous example):

@m23_v2=([@a1],[@a2],[@a3]) 

the difference between 2 ways when backslashes used changing $a[0][0] change $a1[0]. on other hand when brackets used value copied changing $a[0][0] not change $a1[0]. bellow memory addresses of variables should clarify mean:

print \$a1[0] scalar(0x2006c0a0)  print \$m23_v1[0][0] scalar(0x2006c0a0)  print \$m23_v2[0][0] scalar(0x2030a7e8) 

how achieve same in c? i've tried following code:

# include <stdio.h> int main(){   int a1[3] = {1,2,3};   int a2[3] = {4,5,6};   int m23[2][3] = {a1, a2};   printf("%d\n", a1[0]);   printf("%d\n", m23[0][0]); } 

but gives me following compilation warnings:

2d.c: in function ‘main’: 2d.c:4:3: warning: initialization makes integer pointer without cast [enabled default] 2d.c:4:3: warning: (near initialization ‘m23[0][0]’) [enabled default] 2d.c:4:3: warning: initialization makes integer pointer without cast [enabled default] 2d.c:4:3: warning: (near initialization ‘m23[0][1]’) [enabled default] 2d.c:5:3: warning: incompatible implicit declaration of built-in function ‘printf’ [enabled default] 

after execution c code returns following:

1 -1077371888 

questions:

1. why compilation warnings , how modify code rid of them?
2. if given c equivalent backslashed perl version equivalent brackets version (and vice versa)?
3. why -1077371888 instead of 1?

you can use array of pointers equivalent of backslahed version (i.e. @m23_v1):

#include <stdio.h>  int main(void) {     int a1[3] = {1,2,3};     int a2[3] = {4,5,6};      int *m23[2] = {a1, a2};      printf("%d\n", a1[0]);     printf("%d\n", m23[0][0]);      return 0; } 

in code:

int m23[2][3] = {a1, a2}; 

initializer expects filled integers. create two-dimensional array 2 integers: a1, a2. remaining elements initialized zeros. illustrate it, looks like:

int m23[2][3] = {0xaaee33, 0xaaee55, 0, 0, 0, 0}; 

which same as:

int m23[2][3] = {{0xaaee33, 0xaaee55, 0}, {0, 0, 0}}; // 2 rows, 3 columns 

however, a1 not integer. it's name of array, implicitely converted int (after converted pointer, points array's first element). in other words implicitely converting addresses of a1 , a2 2 integers. in fact, such operation illegal in c , such code should not compile -pedantic-errors flag (or equivalent).

what equivalent brackets version (and vice versa)?

the equivalent of braced version define multidimensional array of specific size , copy each element of a1 , a2 arrays it:

#include <stdio.h> #include <string.h>  int main(void) {     int a1[3] = {1,2,3};     int a2[3] = {4,5,6};      int m23[2][3];     memcpy(m23 + 0, a1, sizeof(a1));     memcpy(m23 + 1, a2, sizeof(a2));      printf("%d\n", a1[0]);     printf("%d\n", m23[0][0]);      return 0; }