CODEWITHSUNDEEP
cecho
Imaginary
Imaginary

Reputation: 773

C: Output prints values inside of a variable that is not echoed

I have this very simple code of C that simply must echo values inside the x array, suprisingly, it also echoes the values inside the array y...

#include <iostream.h>
#include <conio.h>
#include <string.h>

int     i;
char    x[3]={'a','b','c'},
        y[3][2]={
             {'a','A'},
             {'b','B'},
             {'c','C'}};
void main(){
    clrscr();
    while(i<strlen(x)) cout << x[i++] << endl;
    getch();
}

Output:

a
b
c
a
A
b
B
c
C

Obviously, the first 3 characters are those that I really intended to echo...
But how about those following characters from array y?

Upvotes: 0

Views: 71

Answers (3)

Imaginary
Imaginary

Reputation: 773

Simply change strlen to sizeof. Why?

  • Arrays are not automatically ended with terminating null character \0
  • The strlen function counts the offset address until \0
  • Using sizeof wil thus count the size alloted for a particular array

The strlen(x) function is supposed to count until it finds the \0, and in this code, it did not.

Upvotes: 0

unwind
unwind

Reputation: 399833

The variable x is not a string, calling strlen() on it leads to undefined behavior.

Accessing out of bounds of the array x leads to undefined behavior too.

You need:

const char *x = "abc";

to make it a valid string (i.e. be terminated by '\0'), or:

const char x[] = { 'a', 'b', 'c', '\0' };

but that's much more verbose so why ever do it that way? If you mean a string (and you do), write it as a string.

You can of course go the other way too, and say "it's a character array, but not a string", but then you can't use strlen() which requires a string:

const char x[] = { 'a', 'b', 'c' };

for(size_t i = 0; i < sizeof x / sizeof *x; ++i)
  printf("%c\n", x[i]);

Upvotes: 7

DaFei
DaFei

Reputation: 1

strlen(x) will return 9 or more, it depended on when it find the end char of string '\0', so the cout will output the data out of the array x 's memory. you can check with the memory, and step by step to debug it.

Upvotes: 0

Related Questions