problems with reacating memory

[baxy77bax]

hi ppl,

i have this problem with reallocating memory. First to mention that I'm a beginner



so the problem is, when i do this :

typedef struct xxx{
	char **test;
} XX;


XX *var;
var = (XX *)malloc(sizeof(XX))
var->test = (char **)malloc(sizeof(char *));
//and then in the loop i would like to extend my var->test 
while(){
var->test = (char **)realloc(var->test,20*sizeof(char *));
}

it does not work (Segmentation fault) if i allocate the sizeof(char *) in the beginning and then try to realloc the pointer by 20 ( keap in mind that a already have some data in the var->test[i] (i = 0..2) )

var->test = (char **)realloc(20*sizeof(char *))

but if i allocate the (

var->test = (char **)malloc(20*sizeof(char *))

) in the beginning then it works (at least i think so).

how do U reallocate the size of the pointer to a char pointer so that i can keap adding characters to my

var->test[i]

arrays


thank you

baxy

[cas]

You say you have data in var->test[i] with i being in the range 0-2 (at least, I think you're saying that). But you only allocated space for one char*, so accessing var->test[1] and [2] is illegal. You very likely destroyed some memory that your allocator depends on.

I'm not sure if you're aware of this, either, but realloc() isn't used (solely) to increase the amount of allocated memory, but rather to allocate a different amount. So:

x = malloc(50);
x = realloc(x, 100);

Now you have 100 bytes, not 150.

Also, in the future, please do not describe a problem by saying "it does not work". This phrase is next to meaningless. You should explain how it doesn't work.

[baxy77bax]

But you only allocated space for one char*, so accessing var->test[1] and [2] is illegal.

Ok, this is embarrassing, thanks for noticing, actually i just wrote that without paying to much attention to what exactly i am writing, but that is the case. I was reallocating the size of sub-arrays (second dimension) but not the first ( at least not correctly) and that is why the 'Segmentation fault' kept appearing over and over again.

Thanks

baxy