CODEWITHSUNDEEP
c++
MikaelCMiller
MikaelCMiller

Reputation: 95

C String Infinite For Loop For Small C[]

Why does c-string length matter when using for loops? Is there an issue with the termination character '\0'?

The following code sends the for loop into a crazy loop that crashes the compiler:

#include <iostream>
#include<cstring>

using namespace std;

int main()
{
    char c[] = "charac";
    int i;

    for (i=0; i < 8 ; i++)
    {
        cout << c[i] << endl;
    }
    return 0;
}

By adding a 't' to my c-string, the code runs perfectly fine:

    char c[] = "charact";
    int i;

    for (i=0; i < 8 ; i++)
    {
        cout << c[i] << endl;
    }

Upvotes: 0

Views: 136

Answers (5)

adilip
adilip

Reputation: 43

c[7] doesn't exist for "charac" as c[6] is the null terminating character. But when you change it to "charact" then c[7] becomes the null terminating character so it runs fine.

Upvotes: 0

Brandon Clements
Brandon Clements

Reputation: 31

You are index past the end of the array. C starts indexing at zero so the last index of a six character string is five. If you include the null terminator then you have six but you are accessing the seventh array position.

Upvotes: 1

user2357112
user2357112

Reputation: 281496

In your first version, there is no character c[7]. You have 7 characters in the array, 6 characters of string and 1 null terminator:

Array:   c h a r a c \0
Indices: 0 1 2 3 4 5 6

Attempting to access anything beyond that is undefined behavior.

In your second version, assuming the code you're running has the t you forgot to put in the posted version, the array has 8 characters, and the loop stays within the bounds of the array.

Upvotes: 2

John Yetter
John Yetter

Reputation: 251

I think that you are stepping past the end of the end of your character array. By adding the extra character, your string is now 7 characters long so the i<8 test works.

Upvotes: 1

Zac Howland
Zac Howland

Reputation: 15870

You have a string of length 7 (6 + null terminator), and are attempting to access an 8th element. This will result in undefined behavior.

Upvotes: 1

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