C- Interaction between pointers, arrays, and structs -

i've been reading on pointers , arrays in c in effort learn how implement vla-ish member of struct. (specifically, need array or array-like object length different between instances of struct defined @ compile-time particular struct instance.)

it seems me though this:

typedef struct example{     unsigned char length;     char *data; }example;  int buildexample(example e, unsigned char l, char * const d){     e.length = l;     e.data = d;     return 0;     //not safe know, fact isn't relevant question. }   main(){     example e;     unsigend char = 5;     char b[] = {1, 2, 3, 4, 5};     buildexample(e, a, b);     int = 0;     while(i < e.length){         printf("%d  %d\n", i, e.b[i]);         i++;     }     printf("%d  %d\n", i, e.b[i]); } 

should result in output:

0  1 1  2 2  3 3  4 4  5 5  unknown value or segfault, not sure 

and various pointers , memory cells , such should go this:

before call buildexample:  example e.data                 b               address 0, 1, 2... |null pointer|         |ptr address 0|      |  1  |  2  |  3  |  4  |  5  |  after call buildexample:  example e.data                  address 0, 1, 2... |ptr address 0|              |  1  |  2  |  3  |  4  |  5  | 

but instead segfault. if swap out e.data b, 'unknown value' outcome (32765, 32766 or 32767, whatever reason), , if swap out e.data new int* c, defined , set equal b in main, same result b, implies me e.data not in fact being set b buildexample.

why not?

when calling buildexample() you're passing copy of e struct created in main(), changes lost when function returns. use pointer instead.

int buildexample(example *e, unsigned char l, char * const d){     e->length = l;     e->data = d;     return 0;     //not safe know, fact isn't relevant question. } 

and when calling:

buildexample(&e, a, b); 

however have other errors such unsigend char = 5; (should unsigned not "unsigend") , trying access element named b (should data).

buildexample(&e, a, b); while(i < e.length){     printf("%d  %d\n", i, e.data[i]);     i++; } printf("%d  %d\n", i, e.data[i]); 

hope helps!