Select Category 
 

C Interview Questions Answers

C Interview Question - 151 : -

What is an lvalue?

C Interview Answer - 151 : -

An lvalue is an expression to which a value can be assigned. The lvalue expression is located on the left side of an assignment statement, whereas an rvalue is located on the right side of an assignment statement. Each assignment statement must have an lvalue and an rvalue. The lvalue expression must reference a storable variable in memory. It cannot be a constant.
 

C Interview Question - 152 : -

Can the sizeof operator be used to tell the size of an array passed to a function?

C Interview Answer - 152 : -

No. There’s no way to tell, at runtime, how many elements are in an array parameter just by looking at the array parameter itself. Remember, passing an array to a function is exactly the same as passing a pointer to the first element.
 

C Interview Question - 153 : -

 I had the definition char a[6] in one source file, and in another I declared extern char *a. Why didn't it work?

C Interview Answer - 153 : -

In one source file you defined an array of characters and in the other you declared a pointer to characters. The declaration extern char *a does not declare an array and therefore does not match the actual definition. The type pointer-to-type-T is not the same as array-of-type-T. Use extern char a[].
 

C Interview Question - 154 : -

What is the difference between far and near?

C Interview Answer - 154 : -

Some compilers for PC compatibles use two types of pointers. near pointers are 16 bits long and can address a 64KB range. far pointers are 32 bits long and can address a 1MB range.
Near pointers operate within a 64KB segment. There’s one segment for function addresses and one segment for data. far pointers have a 16-bit base (the segment address) and a 16-bit offset. The base is multiplied by 16, so a far pointer is effectively 20 bits long. Before you compile your code, you must tell the compiler which memory model to use. If you use a smallcode memory model, near pointers are used by default for function addresses.
That means that all the functions need to fit in one 64KB segment. With a large-code model, the default is to use far function addresses. You’ll get near pointers with a small data model, and far pointers with a large data model. These are just the defaults; you can declare variables and functions as explicitly near or far.
far pointers are a little slower. Whenever one is used, the code or data segment register needs to be swapped out. far pointers also have odd semantics for arithmetic and comparison. For example, the two far pointers in the preceding example point to the same address, but they would compare as different! If your program fits in a small-data, small-code memory model, your life will be easier.
 

C Interview Question - 155 : -

How can you check to see whether a symbol is defined?

C Interview Answer - 155 : -

You can use the #ifdef and #ifndef preprocessor directives to check whether a symbol has been defined (#ifdef) or whether it has not been defined (#ifndef).
Can you define which header file to include at compile time? Yes. This can be done by using the #if, #else, and #endif preprocessor directives. For example, certain compilers use different names for header files. One such case is between Borland C++, which uses the header file alloc.h, and Microsoft C++, which uses the header file malloc.h. Both of these headers serve the same purpose, and each contains roughly the same definitions. If, however, you are writing a program that is to support Borland C++ and Microsoft C++, you must define which header to include at compile time. The following example shows how this can be done:
#ifdef _ _BORLANDC_ _
#include
#else
#include
#endif
 

C Interview Question - 156 : -

Can a variable be both const and volatile?

C Interview Answer - 156 : -

Yes. The const modifier means that this code cannot change the value of the variable, but that does not mean that the value cannot be changed by means outside this code. For instance, in the example in FAQ 8, the timer structure was accessed through a volatile const pointer. The function itself did not change the value of the timer, so it was declared const. However, the value was changed by hardware on the computer, so it was declared volatile. If a variable is both const and volatile, the two modifiers can appear in either order.