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Can a file other than a .h file be included with #include?
The preprocessor will include whatever file you specify in your #include statement. Therefore, if you have the line #include <macros.inc> in your program, the file macros.inc will be included in your precompiled program. It is, however, unusual programming practice to put any file that does not have a .h or .hpp extension in an #include statement. You should always put a .h extension on...
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How are portions of a program disabled in demo versions?
If you are distributing a demo version of your program, the preprocessor can be used to enable or disable portions of your program. The following portion of code shows how this task is accomplished, using the preprocessor directives #if and #endif: int save_document(char* doc_name) { #if DEMO_VERSION printf(“Sorry! You can’t save documents using the DEMO version of this program!n”); return(0); #endif...
kbjarnason
- Jul 2nd, 2010
The example given has a flaw. It essentially works like this:void SaveFile( char *fname, void *data ){#if DEMO puts( "Nope, sorry, no can do" ); return;#endif &n...
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Is it better to use a macro or a function?
The answer depends on the situation you are writing code for. Macros have the distinct advantage of being more efficient (and faster) than functions, because their corresponding code is inserted directly into your source code at the point where the macro is called. There is no overhead involved in using a macro like there is in placing a call to a function. However, macros are generally small and...
Manan Jadhav
- May 4th, 2011
macros are usually preferred when the code is very small... They are usually faster as compared to the functions as the code itself is expanded in the original code where as for function there is a co...
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How can type-insensitive macros be created?
A type-insensitive macro is a macro that performs the same basic operation on different data types. This task can be accomplished by using the concatenation operator to create a call to a type-sensitive function based on the parameter passed to the macro. The following program provides an example: #include <stdio.h> #define SORT(data_type) sort_ ## data_type void sort_int(int** i); void sort_long(long**...
abhimanipal
- Jan 30th, 2010
There is small bug in the above programWhen the macro is define it is written as SORT, but when it is used it is written as sortThis will give an error
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How do you override a defined macro?
You can use the #undef preprocessor directive to undefine (override) a previously defined macro.
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What is the difference between a string copy (strcpy) and a memory copy (memcpy)? When should each be used?
The strcpy() function is designed to work exclusively with strings. It copies each byte of the source string to the destination string and stops when the terminating null character () has been moved. On the other hand, the memcpy() function is designed to work with any type of data. Because not all data ends with a null character, you must provide the memcpy() function with the number of bytes you...
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How can I convert a string to a number?
The standard C library provides several functions for converting strings to numbers of all formats (integers, longs, floats, and so on) and vice versa. The following functions can be used to convert strings to numbers: Function Name Purpose atof() Converts a string to a double-precision floating-point value. atoi() Converts a string to an integer. atol() Converts a string to a long integer....
rasmiranjanbabu
- Jul 5th, 2007
/*Let take an example*/main(){char rasmi="111";int ranjan;ranjan=atoi(rasmi);printf("n This is Rasmi Ranjan Nayak's Reply %d n", ranjan);}
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What is indirection?
If you declare a variable, its name is a direct reference to its value. If you have a pointer to a variable, or any other object in memory, you have an indirect reference to its value.
Sandhya.Kishan
- Mar 28th, 2012
Indirection operator (denoted by *) is a unary operator which include pointer variables. It operates on a pointer variable,and returns a value equivalent to the value at the pointer address. Example:...
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Is NULL always defined as 0?
NULL is defined as either 0 or (void*)0. These values are almost identical; either a literal zero or a void pointer is converted automatically to any kind of pointer, as necessary, whenever a pointer is needed (although the compiler can’t always tell when a pointer is needed).
kbjarnason
- Jul 2nd, 2010
In a pointer context, an integer constant value of 0 (cast to void * or not) becomes a null pointer constant. If assigned to a pointer, comparing the pointer to NULL will evaluate as true.That i...
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When would you use a pointer to a function?
Pointers to functions are interesting when you pass them to other functions. A function that takes function pointers says, in effect, “Part of what I do can be customized. Give me a pointer to a function, and I’ll call it when that part of the job needs to be done. That function can do its part for me.” This is known as a “callback.” It’s used a lot in graphical user interface libraries, in which...
abhimanipal
- Jan 30th, 2010
Another application could be when the function is not located in the code segment. Many time the size of the Source code is greater than 64 KB. In such a scenario if we want to call a function, we have to use a far pointer to call that function. Not sure though
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Is it better to use malloc() or calloc()?
Both the malloc() and the calloc() functions are used to allocate dynamic memory. Each operates slightly different from the other. malloc() takes a size and returns a pointer to a chunk of memory at least that big: void *malloc( size_t size ); calloc() takes a number of elements, and the size of each, and returns a pointer to a chunk of memory at least big enough to hold them all: void *calloc(...
Sandhya.Kishan
- Mar 28th, 2012
Malloc() and calloc() are used to allocate memory blocks dynamically.malloc() is a bit faster since it does not initialize the allocated memory blocks to as it is done by calloc() function.Hence it is better to use malloc() then calloc().
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Can the size of an array be declared at runtime?
No. In an array declaration, the size must be known at compile time. You can’t specify a size that’s known only at runtime. For example, if i is a variable, you can’t write code like this: char array[i]; /* not valid C */ Some languages provide this latitude. C doesn’t. If it did, the stack would be more complicated, function calls would be more expensive, and programs would run a lot slower. If you...
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What is the heap?
The heap is where malloc(), calloc(), and realloc() get memory. Getting memory from the heap is much slower than getting it from the stack. On the other hand, the heap is much more flexible than the stack. Memory can be allocated at any time and deallocated in any order. Such memory isn’t deallocated automatically; you have to call free(). Recursive data structures are almost always implemented with...
psjetha
- Sep 1st, 2009
Heap is a dynamic memory of main memory. In main memory there are several type of memory management like fixed, static, dynamic (it is just memory area which can be used by any task or process but it ...
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What is the difference between NULL and NUL?
NULL is a macro defined in <stddef.h> for the null pointer. NUL is the name of the first character in the ASCII character set. It corresponds to a zero value. There’s no standard macro NUL in C, but some people like to define it. The digit 0 corresponds to a value of 80, decimal. Don’t confuse the digit 0 with the value of ‘’ (NUL)! NULL can be defined as ((void*)0), NUL as ‘’.
abhimanipal
- Jan 30th, 2010
When we have a pointer variable of the sortchar* pWe often want to initialize it to 0, to ensure it does not point anywhere. We do this bychar* p=0Many programmers do not feel comfortable with the fac...
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Can math operations be performed on a void pointer?
No. Pointer addition and subtraction are based on advancing the pointer by a number of elements. By definition, if you have a void pointer, you don’t know what it’s pointing to, so you don’t know the size of what it’s pointing to. If you want pointer arithmetic to work on raw addresses, use character pointers.
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How do you print an address?
The safest way is to use printf() (or fprintf() or sprintf()) with the %P specification. That prints a void pointer (void*). Different compilers might print a pointer with different formats. Your compiler will pick a format that’s right for your environment. If you have some other kind of pointer (not a void*) and you want to be very safe, cast the pointer to a void*: printf( “%Pn”, (void*) buffer...
paulson paul chambakottukudyil
- Apr 24th, 2006
I tried both %p and %Fp. There is no difference, atleast in MS visual studio. Both are printing the same value.
ravisankar2
- Feb 19th, 2006
THIS IS FROM c.ravi sankar reddy,hai to ALL........we can print the address of a variable or a function using the following specifiers %u,%p here %u prints address in decimal form and %p prints in hex...
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Why should I prototype a function?
A function prototype tells the compiler what kind of arguments a function is looking to receive and what kind of return value a function is going to give back. This approach helps the compiler ensure that calls to a function are made correctly and that no erroneous type conversions are taking place.
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Is using exit() the same as using return?
No. The exit() function is used to exit your program and return control to the operating system. The return statement is used to return from a function and return control to the calling function. If you issue a return from the main() function, you are essentially returning control to the calling function, which is the operating system. In this case, the return statement and exit() function are similar....
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What is storage class and what are storage variable ?
A storage class is an attribute that changes the behavior of a variable. It controls the lifetime, scope and linkage.There are five types of storage classes 1)auto 2)static 3)extern 4)register 5)typedef
Sandhya.Kishan
- Mar 28th, 2012
Storage class are used to define the lifetime and scope of a function or available.There are four storage classes namely auto,static,register and extern storage classes. Storage variables are the vari...
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Differentiate between a linker and linkage?
A linker converts an object code into an executable code by linking together the necessary build in functions. The form and place of declaration where the variable is declared in a program determine the linkage of variable.
Sandhya.Kishan
- Mar 28th, 2012
Linker are used to convert the object code to executable codes where as linkage to a variable determines the deceleration of the variables declared in the given program.
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