[转]国外嵌入式面试题

Embedded System Interview Questions:

1.            Can structures be passed to the functions by value?

2.            Why cannot arrays be passed by values to functions?

3.            Advantages and disadvantages of using macro and inline functions?

4.            What happens when recursion functions are declared inline?

5.            Scope of static variables?

6.            Difference between object oriented and object based languages?

7.            Multiple inheritance - objects contain howmany multiply inherited ancestor?

8.            What are the 4 different types of inheritance relationship?

9.            How would you find out the no of instance of a class?

10.       Is java a pure object oriented language? Why?

11.       Order of constructor and destructor call in case of multiple inheritance?

12.       Can u have inline virtual functions in a class?

13.       When you inherit a class using private keyword which members of base class are visible to the derived class?

14.       What is the output of printf("\nab\bcd\ref"); -> ef

15.       #define cat(x,y) x##y concatenates x to y. But cat(cat(1,2),3) does not expand but gives preprocessor warning. Why?

16.       Can you have constant volatile variable? Yes, you can have a volatile pointer?

17.       ++*ip increments what? it increments what ip points to

18.       Operations involving unsigned and signed — unsigned will be converted to signed

19.       a+++b -> (a++)+b

20.       malloc(sizeof(0)) will return — valid pointer

21.       main() {fork();fork();fork();printf("hello world"); } — will print 8 times.

22.       Array of pts to functions — void (*fptr[10])()

23.       Which way of writing infinite loops is more efficient than others? there are 3ways.

24.       # error — what it does?

25.       How is function itoa() written?

26.       Who to know wether systemuses big endian or little endian format and how to convert among them?

27.       What is interrupt latency?

28.       What is forward reference w.r.t. pointers in c?

29.       How is generic list manipulation function written which accepts elements of any kind?

30.       What is the difference between hard real-time and soft real-time OS?

31.       What is interrupt latency? How can you recuce it?

32.       What is the differnce between embedded systems and the system in which rtos is running?

33.       How can you define a structure with bit field members?

34.       What are the features different in pSOS and vxWorks?

35.       How do you write a function which takes 2 arguments - a byte and a field in the byte and returns the value of the field in that byte?

36.       What are the different storage classes in C?

37.       What are the different qualifiers in C?

38.       What are the different BSD and SVR4 communication mechanisms

  Persional Prospectives:

1.            Q1. No they are always passed by reference. Think. Size of structure can be arbitrarily large.
Q2. Same as above.
Q5. Lifetime of process.
Q9. Declare a static variable, class variable, and increment(decrement) for every constructor (destructor) called.
Q11. Constructor. Base to current. Destructor. current to base. Both are done recursuively.
Q13. NONE
Q14. $> acd
ef
->ef is wrong, what happened to acd?
Q16. You can have a constant pointer to a volatile variable but not a constant volatile variable.
Q26. Write a union of int and 2 chars. Store as int retrieve as chars.
Q 27. Time taken between INT req and INT service.
Q33. Study Let us C, Yeshwant Kanetkar

Tech Interviews comment by

2.            Q. 13
Answer posted is wrong.
Public & protected members of base class will be visible to derived class, but not its objects.

Tech Interviews comment by Sumeet

3.            Q1 - YES, a complete structure can be passed. Regarding the size, it is true that they can be very large and hence it is not a good practice to do so. In any case, one can do if one wants to.

Tech Interviews comment by

4.            Q3. When using macro you can’t use data type while passing it. But in Inline function you can have data types so that it can be checked.
e.g MACRO : ADD(a,b)
INLINE : inline void Add(int a,int b );

Tech Interviews comment by VijayaKumar

5.            Q1. Yes structure can be passed by value but the overhead of copying large values will be there. hence not usable. We should pass it by pointer.
Q2. Individual element can be passed by value of course. But not whole array.
Q5. It is alive lifetime of process, and its scope is limited to function in which it is defined.
file1.c
**********
static int i;
void main()
{
……..
}
file2.c
**********
extern int i; //error

If declared global then it is visible in that file only.
Q6. Object oriented language have Inheritance, polymorphism etc. But object based language only deal with object.
Q7. If
class D:public A,B,C
{}
then three ancestors
Q8. public ,private, protected, virtual
Q30. Hard RTS is having deadline defined and it is life critical ,should be reliable. late answer is wrong answer. in Soft RTS,process time should be predictable and reliable.

Tech Interviews comment by Pawan Kumar

6.            Q36.What are the different storage classes in C?
A:Auto,Register,Static,Extern

Tech Interviews comment by MKS

7.            Q5 Scope of static variables is only within the block where it is declared.
But the lifetime is till the process is running

Tech Interviews comment by Satish Parande

8.            Questin???

How can we dynamically allocate memory without using malloc() or calloc() or realloc()?Explain in Breif.

Can any one help in finding this answer to this question……

Tech Interviews comment by Midhun V

9.            In Java, we place even the Main() function inside a CLASS.
But it is not the case with C++.

So, i think this is one of the answers you can say, JAVA is Fully Obejct Oriented.

Tech Interviews comment by vsvraju

10.       Q11 : Base-class constructors are called in the order in which inheritance is specified in the derived-class definition. The order in which the Base-class constructors are specified in the derived-class member initializer list does not effect the order of construction.

Tech Interviews comment by vsvraju

11.       Q 12:
Yes we can have.
you are never guaranteed that a routine is inlined. It is only a suggestion to the compiler. If
the routine is either too complicated or a virtual function,then a static copy of the routine will be placed in the compiled module. Thus, a routine that was coded as inline may cause a performance degradation because it may consume much more space when it is not physically inlined.
With a virtual function, a copy of that routine will be created for every module that has at least one instantiation of that class.

Q 13:
NONE.
None of the Public, Protected and Private data members are visible.

Q 16:
YES. We can have a const volatile variable.
a volatile variable is a variable which can be changed by the extrenal events (like an interrput timers will increment the voltile varible. If you dont want you volatile varibale to be changed then declare them as “const volatile”.

Q 17.
I will explain this with an example:

int a = 10;
int *p = &a;
// suppose &a = 4010 (address of a)

Because both ++ and * are unary operators, the are calculated from right to left –> ++ (*p)

++*p will inrement 4010 by 4 (int size) -> ++*p will have the value 4014.

Q 21:
It will print 8 times. Because, each fork will print twice.
if u flush, (using “fflush”), then it will be printed only once. thats is you need to flush the iostreams.

Q 30:

In Hard RTOS the latency should be less the 20ns (nano sec)
in Soft RTOS the latency range 3ns - 20ns is also acceptable.

Tech Interviews comment by vsvraju

12.       I THINK A BALOON CAN HAVE TO MUCH ELECTRICITY

Tech Interviews comment by

13.       Java is not a pure object oriented language as “everything” in java is not an object. It still has primitive data types such as int, char, etc. which are NOT objects. Ruby is an example of a pure object oriented language, where “everything” is an object, even int.

Tech Interviews comment by Karan

14.       16. It is possible to have “const volatile” declaration. This indicates that the variable defined like this is not possible to change within that context. It can be changed by an external event. const declaraion just says that it will be readonly within the context, that area can be modified by an interrupt routine or another process.

18. Operations involving unsigned and signed - The signed data will be converted to unsigned - Refer arithemetic conversion rules in K&R

24. #error is used for displaying an error while compilation. for eg.

#ifdef ABC
printf(”ABC”);
#else
#ifdef DEF
printf(DEF);
#else
#error “Declaration not done”
#endif

30. Hard RTOS is system which will be having major problems if the specified time limit is crossed. For eg. missiles
Soft RTOS is systems which will not be having major problems if the specified limit is crossed. For eg. real time audio steaming.
But for both exceeding the time limit is concidered as error.

31. Interrupt latency is the time period between interrupt on the pin to the execution of 1st instuction in the interrupt routine. THis will depend upon the processor. If the execution time for the instruction is less (like in RISC) this time will also be less. If register storage is required the time will be less in the processors in which remapping of registers is present as this can be done in a single instruction.

32. RTOS systems are embedded systems with time criticality.
33.

Tech Interviews comment by deepak

15.       What is interrupt latency?
It is the time interval between an interrupt has occured till the time it has been serviced.
Mathematically:

Int(lat)= rt+pt+dt

where rt=recognition time
pt=process time
dt=dispatch time

Tech Interviews comment by

16.       Q. Write a function to reverse contents in a single linked list without reversing the links?
Can anyone pls help me out?

Tech Interviews comment by

17.       Q.Can we have a constant volatile variable?

Soln: YES.We can have a const volatile variable.
Volatile variable is one which can be changed by user,ie programmer as well as by the external events.If we declare it as const volatile,then user cannot change but can be changed by the hardware.

Tech Interviews comment by

18.       20.
malloc(sizeof(0)) will return — valid pointer
yes. sizeof(0) –> int size and it is 4

25.
itoa(…)
itoa(pointer to storage buffer,int to convert, base(eg.binary,oct,hex,dec))

33.
typedef struct regset{
unsigned char onebit:1;
unsigned char twobit:2;
….
}regset;

Tech Interviews comment by Ramesh.V

19.       i have an query regarding , interupts in Embedded systems

can we use the interrupt function call same as ordinary function,i.e. can we pass arguments and return values from an ISR routine.

Tech Interviews comment by Sushil Rana

20.       what happens when
we put an infinite loop using for

for(;;)
what is the condition expression value by default.

Tech Interviews comment by

21.       Write a function to reverse contents in a single linked list without reversing the links?
Can anyone pls help me out?

Count number of nodes in the linear linked list. Let say cnt is the number of nodes and index = 0. You can swap content of index th node and cnt-index th node, each time increment index by 1. All the contents will be reversed.

Tech Interviews comment by Hetal

22.       Scope of static variables?
scope of static variables is limited to the local function in which it is defined and to the functions calling the stattic variable.

Tech Interviews comment by Guneet

23.       How virtual tables are created in case of abstract classes? Is it the same as in non-abstract classes? Virtual tables r created on stack or Heap?

Tech Interviews comment by Satish Parande

24.       why only reference is passed as a parameter in Copy constructor? why not address?

Tech Interviews comment by Satish Parande

25.       is it possible to call delete from the class member function ?

Tech Interviews comment by Mrinmay Biswas

26.       q.3.
—- Inline is only a request that may be rejected also based on optimization policies,while macro is immediately replaced before compilation.
—- type checking is not possible in Macros, but in inline its possible.

Tech Interviews comment by Praveen