Hello I can't figure out why a) this code errors on the last copy and b) in the debugger it shows picture[0] containing 0 to 4 then containing 1 to 4 (see picture1)
char picture[5][5];
strcpy(picture[0], "#####");
strcpy(picture[1], "#####");
strcpy(picture[2], "#####");
strcpy(picture[3], "#####");
strcpy(picture[4], "#####");
When xcode errors it shows the following
In C strings ends with the character \0. So you shall reserve space for them by declaring the array as:
char picture[5][6];
When you declare char str[n] it means n-1 chars are reserved for you. While the last one is a '\0' char (terminator). If you overwrite the '\0' char, it goes on printing till it finds the '\0' in memory.
So modify char picture[5][5]; to char picture[5][6];
You forgot that you need a null byte to terminate the strings. (In fact, your last strcpy() writes outside the bounds of the array, invoking undefined behaviour.) Use:
char picture[5][6] = { "#####", "#####", "#####", "#####", "#####", };
This saves on the strcpy() calls too.
I commented:
The compiler might well generate warnings if you change the 6 to 5, but I think it is required to allow the initializers (even though it would have to drop the terminating null bytes). But it is a warning that you'd want to fix; it is showing a genuine problem.
In fact, GCC 4.8.2 doesn't even warn about the issue under fairly stringent compilation options.
Compilation:
gcc -O3 -g -std=c11 -Wall -Wextra -Werror ols.c -o ols
Code:
#include <stdio.h>
static char picture1[5][5] = { "#####", "#####", "#####", "#####", "#####", };
static char picture2[5][6] = { "#####", "#####", "#####", "#####", "#####", };
int main(void)
{
for (int i = 0; i < 5; i++)
printf("%s\n", picture1[i]);
for (int i = 0; i < 5; i++)
printf("%s\n", picture2[i]);
return 0;
}
Output:
#########################
####################
###############
##########
#####
#####
#####
#####
#####
#####
Whenever you are using a function from strings.h, make sure you take care of "\0", otherwise you will always get unexpected output at the end of the string(esp. when printing with %s). The compiler wont give any warnings because it wouldn't find anything wrong. When you are printing with %s the compiler will look for "\0", and keep printing until then when you run the program. In fact when you are coping using strncpy, if have an array size 9 and you only use 5, the rest 4 will have null stored in them.
