C Questions and Answers – DMA Functions, Memory Leak, Dangling Pointers – 2

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This set of C Multiple Choice Questions & Answers (MCQs) focuses on “DMA Functions, Memory Leak, Dangling Pointers – 2”.

Pre-requisite for this C MCQ set: Advanced C Programming Video Tutorial.

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1. What will be the output of the following C code if it is executed on a 32 bit processor?

#include<stdio.h>
#include<stdlib.h>
int main()
{
    int *p;
    p = (int *)malloc(20);
    printf("%d\n", sizeof(p));
    free(p);
    return 0;
}

a) 2
b) 4
c) 8
d) Junk value
View Answer

Answer: b
Explanation: The size of a pointer is 2 bytes on a 16 bit platform, 4 bytes on a 32 bit platform and 8 bytes on a 64 bit platform.
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2. The number of arguments taken as input which allocating memory dynamically using malloc() is ___________
a) 0
b) 1
c) 2
d) 3
View Answer

Answer: b
Explanation: An example of memory allocated using malloc():
(int*)malloc(3*sizeof(int)
It is clear from the above example that malloc() takes only one argument as input, that is the number of bytes to be allocated.
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3. Suppose we have a one dimensional array, named ‘x’, which contains 10 integers. Which of the following is the correct way to allocate memory dynamically to the array ‘x’ using malloc()?
a) x=(int*)malloc(10);
b) x=(int*)malloc(10,sizeof(int));
c) x=malloc(int 10,sizeof(int));
d) x=(int*)malloc(10*sizeof(int));
View Answer

Answer: d
Explanation: According to the syntax of malloc, the correct way to do the specified operation is: x=(int*)malloc(10*sizeof(int)); This operation can also be performed using calloc(). In that case, the method will be: x=(int*)calloc(10,sizeof(int));

4. What will be the error (if any) in the following C code?

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#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int main()
{
    char *p;
    *p = (char)calloc(10);
    strcpy(p, "HELLO");
    printf("%s", p);
    free(p);
    return 0;
}

a) No error
b) Error in the statement: strcpy(p,”HELLO”);
c) Error in the statement: *p=(char)calloc(10);
d) Error in the statement: free(p);
View Answer

Answer: c
Explanation: The syntax for dynamically allocating memory using calloc() is incorrect. Hence, this code results in an error. The correct syntax for calloc is: void*calloc(size_t n, size_t size);
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5. If malloc() and calloc() are not type casted, the default return type is ___________
a) void*
b) void**
c) int*
d) char*
View Answer

Answer: a
Explanation: If malloc() and calloc() are not type casted, they return a pointer of the type void.

6. Pick out the correct statement with respect to the heap.
a) Local variables are stored on the heap
b) Static variables are stored on the heap
c) Heap is the data structure that is used to implement recursive function calls
d) Everything on the heap is anonymous
View Answer

Answer: d
Explanation: Local variables are stored on the stack. Static variables are stored in the permanent storage area. Stack is the data structure used to implement recursive function calls. Hence, it is true that everything on the heap is anonymous.

7. What will be the output of the following C code? (Given that the size of array is 4 and new size of array is 5)

#include<stdio.h>
#include<stdlib.h>
main()
{
    int *p,i,a,b;
    printf("Enter size of array");
    scanf("%d",&a);
    p=(int*)malloc(a*sizeof(int));
    for(i=0;i<a;i++)
    printf("%d\n",i);
    printf("Enter new size of array");
    scanf("%d",&b);
    realloc(p,b);
    for(i=0;i<b;i++)
    printf("%d\n",i);
    free(p);
}

a)

   1234
   12345

b) Error
c)

   0123
   01234

d)

   0123
   12345
View Answer
Answer: c
Explanation: In the above code, we are reallocating memory. When the size of the array is 4, the output is 0123. When the size of the array is changed to 5, the output is 01234. Hence, the output is:
0123
01234
 
 

8. When the pointer is NULL, then the function realloc is equivalent to the function ___________
a) malloc
b) calloc
c) free
d) alloc
View Answer

Answer: a
Explanation: If pointer is NULL, the call to the function realloc is equal to malloc(size), for any value of size. If size is equal to zero, then the pointer is not NULL and the call is equivalent to free(pointer).

9. Garbage collector frees the programmer from worrying about ___________
a) Dangling pointers
b) Creating new objects
c) Memory leak
d) Segmentation errors
View Answer

Answer: c
Explanation: A garbage collector is a program that automatically removes unwanted data held temporarily in the memory during processing. Hence it frees the programmer from worrying about memory leaks.

10. If the space in memory allocated by malloc is not sufficient, then an allocation fails and returns ___________
a) NULL pointer
b) Zero
c) Garbage value
d) The number of bytes available
View Answer

Answer: a
Explanation: A NULL pointer is returned when the memory allocated by malloc dynamically is insufficient.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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