Thread: int to char and back

Hi,

I'm trying to add a int to the first four bytes of a char * and then later on I have to extract the int from the char *.
Example

char *foo = " number";
int num = 123456;
memcpy(foo,&num,4);


.........

int num2;
memcpy(num2,foo,4);


But this seems to segfault. What am I doing wrong?

hashbang

In this example, at least, foo is not writable memory (by you). Does it work if you use char foo[] instead?

So using malloc should work? The actuall pinter is malloc'd memory.

int a,b;
char *foo = malloc(sizeof(char) * 100);
int num = 123456;
memcpy(foo,&num,4);

memcpy(a,foo,4);
b = atoi(a);
printf("%d\n", b);
return 0;

And how do you expect memcpy(a, foo, 4) to work? Do you notice how your compiler complains bitterly about that line?

Yes it does, but I am not sure what I am missing.

a is not a memory address.

ah...


memcpy(&a,foo,4);

Right. But somehow I don't think you're gonna get what you wanted. Mixing binary and ASCII like that. or maybe it is.

you might be right as it does not seem too work.

What happens if, instead of printf("%d", b) you do printf("%d",a)?

that works. Thanks. I thought atoi would be needed after storing it in the char *.

Storing it in a char * isn't magic -- or, more to the point, it isn't sprintf.