Problem with strcpy

[TommyFeticini]

#include <stdio.h>
#include <string.h>

int main(int argc, char *argv[]){

//Declaring Variables
char buffer_one[1], buffer_two[1];

strcpy(buffer_one,"1");
strcpy(buffer_two,"1");

printf("[BEFORE] buffer_two is at address %p, and is \'%s\'\n",buffer_two, buffer_two);
printf("[BEFORE] buffer_one is at address %p and is \'%s\'\n",buffer_one, buffer_one);

Can't seem to figure out why this doesn't work. These are my results:


[BEFORE] buffer_two is at address 0x7fff955b636e, and is '1'
[BEFORE] buffer_one is at address 0x7fff955b636f and is ''


O and Please and Thank you for any explanation.
O, just in case I'm using gcc

Target: x86_64-linux-gnu
gcc version 4.4.5 (Ubuntu/Linaro 4.4.4-14ubuntu5)

[TheBigH]

You need to give your arrays enough space to contain the string AND the terminating \0 character at the end.

[quzah]

Plus, it doesn't do anything to the address of the variable. That's always going to be the same. It's what it contains that changes.


Quzah.

[TommyFeticini]

So the reason that the buffer_one isn't taking 1 is because I'm not terminating the char array? I mean I only want one byte ie the character 1 in the char array.

The size of the array should be enough to take on just '1' right?

The problem is that
strcpy(buffer_one,"1");
isn't taking on the value of 1.

[Adak]

The size of the array is enough to hold '1', but that isn't what you asked it to hold. You asked it to hold "1", which is two char's: the 1 and the '\0' (end of string marker char).

And that's a problem.

[TommyFeticini]

AHHHHHHH! Thanks. Big help. Still pretty new, testing bounds.

[TheBigH]

It might give you a better insight into how strings and pointers to strings if you understand exactly why your original code did what it did. Buffer_one has the value 0x7fff955b636f and Buffer_two has the value 0x7fff955b636e, which are addresses in memory. Now let's look at what is actually in those addresses after setting buffer_one but before setting buffer_two:

Address:     636e   636f   6370
Contents:     ?      '1'   '\0'

We haven't touched 636e yet so we don't know what's there, but the next two addresses contain the code for symbol '1' and the end-of-string marker '\0' respectively. Now let's set buffer_two, which begins at 636e. So 636e will contain '1' and the next address, 636f, will contain '\0'- overwriting the '1' that was there before:

Address:     636e   636f   6370
Contents:     '1'   '\0'   '\0'

Now when you attempt to print buffer-two, it will work as expected because it begins with a '1' and ends with a '\0' just like it should. But attempting to print buffer_one, which starts at 636f, will return the empty string because it now begins with '\0'. Buffer_two has interfered with buffer_one because you had only allocated enough space for one character but attempted to store two and so the two strings have overlapped.