Property of external variable to be accessed by any source file is called by C90 standard as:
Answer: A
Correct answer: external linkage
Linkage is the term for whether a name refers to the same object across translation units; scope is where a name is visible within one. A file-scope variable has external linkage - the same object however many files declare it.
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What is the output of this C code?
void main()
{
m();
}
void m()
{
printf("hi");
m();
}
Answer: C
Correct answer: Infinite hi
m calls itself as its last action, with no condition to stop it - unbounded recursion. It prints hi each time, so the output repeats until the stack is exhausted and the program crashes.
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Which part of the program address space is p stored in the code given below?
int *p = NULL;
int main()
{
int i = 0;
p = &i;
return 0;
}
Answer: B
Correct answer: Data segment
p is a file-scope variable with an explicit initialiser, so it goes in the data segment, which holds initialised statics and whose contents come from the executable file. (Strictly, a pointer initialised to NULL is all-zero and many toolchains put it in BSS after all; the distinction the question is drawing is between explicitly initialised and not.)
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What is the output of this C code?
int x;
void main()
{
printf("%d", x);
}
Answer: D
Correct answer: 0
A variable at file scope has static storage duration, and every such object is zero-initialised before the program starts - it is not left holding junk, as an uninitialised automatic variable would be. So the value printed is 0.
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Which of the following is an external variable?
int func (int a)
{
int b;
return b;
}
int main()
{
int c;
func (c);
}
int d;
Answer: D
Correct answer: d
d is declared at file scope, so it is the external variable - even though it appears at the end of the file, which merely limits how much of the file can see it. a is a parameter, and b and c are locals; all three are automatic.
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What is the output of this C code?
void main()
{
m();
void m()
{
printf("hi");
}
}
Answer: B
Correct answer: Compile time error
m is defined inside main, which standard C forbids - and it is also called before its definition is reached. The compiler rejects the program.
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What is the output of this C code?
void foo();
int main()
{
void foo(int);
foo();
return 0;
}
void foo()
{
printf("2 ");
}
Answer: B
Correct answer: Compile time error
Here the two disagree. The declaration in scope says void foo(int), so foo() is called with too few arguments; and the definition, void foo(), conflicts with it as well. Either fault alone is enough for the compiler to reject the program.
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Which of the following is not accepted in C?
Answer: C
Correct answer: static static int a; //a static variable prefixed with static
A storage class specifier may appear only once in a declaration, so static static is rejected. The other two are legal: static a = 10; relies on the old implicit int, and static int func(int); declares a function with internal linkage.
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Can we use a function as a parameter of another function? [ Eg: void wow(int func()) ]
Answer: C
Correct answer: Yes, but we call the function again to get the value, not as convenient as in using variable
C does allow it: a parameter written as a function is adjusted to a pointer to that function, so void wow(int func()) means void wow(int (*func)()). But what is passed is the function itself, not a value - so inside wow you must call it to obtain anything, which is less convenient than passing the value. This is the mechanism behind callbacks, such as the comparison function given to qsort.
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