GATE | GATE CS Mock 2018 | Question 49

Consider the following code. The function myStrcat concatenates two strings. It appends all characters of b to end of a. So the expected output is “Geeks Quiz”. The program compiles fine but produces segmentation fault when run.

void myStrcat(char *a, char *b)
{
    int m = strlen(a);
    int n = strlen(b);
    int i;
    for (i = 0; i <= n; i++)
       a[m+i]  = b[i];
}

int main()
{
    char *str1 = "Geeks ";
    char *str2 = "Quiz";
    myStrcat(str1, str2);
    printf("%s ", str1);
    return 0;
}

Which of the following changes can correct the program so that it prints “Geeks Quiz”?
(A) char *str1 = “Geeks “; can be changed to char str1[100] = “Geeks “;
(B) char *str1 = “Geeks “; can be changed to char str1[100] = “Geeks “; and a line a[m+n-1] = ‘\0’ is added at the end of myStrcat
(C) A line a[m+n-1] = ‘\0’ is added at the end of myStrcat
(D) A line ‘a = (char *)malloc(sizeof(char)*(strlen(a) + strlen(b) + 1)) is added at the beginning of myStrcat()


Answer: (A)

Explanation: When str1 is declared as character pointer, it is stored in read-only block of memory so it can not be modified.

See following for a detailed explanation – https://www.geeksforgeeks.org/storage-for-strings-in-c/

Option (A) is correct.


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