GATE CS 2024 Set 2 Q.33: Pointers, Arrays and Strings

Consider the following C function definition.

int fX(char *a){
    char *b = a;
    while(*b)
        b++;
    return b - a;}

Which of the following statements is/are TRUE?

The function call fX("abcd") will always return a value

Assuming a character array c is declared as char c[] = "abcd" in main(), the function call fX(c) will always return a value

The code of the function will not compile

Assuming a character pointer c is declared as char *c = "abcd" in main(), the function call fX(c) will always return a value

Official answer and solution

Official answer: A, B and D
From: Official GATE 2024 answer key

Solution

Observe that fX only reads the null-terminated string without modifying it, and computes its length via pointer subtraction b - a.

The function fX(char *a) is a standard implementation of strlen: it initializes b = a, increments b until *b == '\0', and returns the number of characters b - a.

Because fX only reads characters through b and never writes to *b or *a, passing a string literal directly (fX("abcd") in A), a modifiable character array (char c[] = "abcd" in B), or a pointer to a string literal (char *c = "abcd" in D) is completely valid and always returns 4.
The function compiles without any error (C is FALSE).

Final answer

Options (A), (B), (D)

Common trap

Thinking that passing a string literal to char *a causes undefined behavior even when the function never modifies the string.

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

Source

Paper: GATE 2024 Computer Science and Information Technology - Set 2 (CS2)
Question: 33 of 65
Section: Computer Science and Information Technology

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