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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 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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Is it better to use a pointer to navigate an array of values,or is it better to use a subscripted array name?
It’s easier for a C compiler to generate good code for pointers than for subscripts.
kbjarnason
- Jul 2nd, 2010
The only "better" is what is more readable and maintainable and sensible to the people reading and writing the code.Any compiler worth having won't care either way, and will generally produce identical or equivalently performing code in each case.
abc
- Sep 15th, 2006
If its linear access it better to use pointers otherwise array name. Array names are faster since it can be used the subscription like a[10].
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What is the benefit of using #define to declare a constant?
Using the #define method of declaring a constant enables you to declare a constant in one place and use it throughout your program. This helps make your programs more maintainable, because you need to maintain only the #define statement and not several instances of individual constants throughout your program. For instance, if your program used the value of pi (approximately 3.14159) several...
kbjarnason
- Jul 2nd, 2010
I see examples such as #define PI 3.1415, which show _how_ you can use a define to declare a constant, but don't exactly explain _why_ you'd want to do this, rather than, say, const double PI ...
janhavibend
- Jul 24th, 2008
When you define constant variable there is possiblity that it's value may get changed in the program accidently by use of say pointer, but if you define constant by #define it's value can't be changed. This is also one of the benifit of using #define.
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What is the quickest sorting method to use?
The answer depends on what you mean by quickest. For most sorting problems, it just doesn’t matter how quick the sort is because it is done infrequently or other operations take significantly more time anyway. Even in cases in which sorting speed is of the essence, there is no one answer. It depends on not only the size and nature of the data, but also the likely order. No algorithm is best in all...
kbjarnason
- Jul 2nd, 2010
One should point out that quicksort can, on some data sets, degenerate to an O(n^2) sort - meaning the next ice age may arrive before your sort finishes. There is, kicking around on the net some...
agni_suresh896
- Apr 19th, 2007
The algorithms which follows divide and qunquer technique provides fastest implementation.
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When should a type cast not be used?
A type cast should not be used to override a const or volatile declaration. Overriding these type modifiers can cause the program to fail to run correctly. A type cast should not be used to turn a pointer to one type of structure or data type into another. In the rare events in which this action is beneficial, using a union to hold the values makes the programmer’s intentions clearer.
kbjarnason
- Jul 2nd, 2010
And it should never, ever, EVER be used to cast the return from malloc, at least in C (and if you're using C++, why are you using malloc?)
shivakumara.madegowda
- Mar 20th, 2007
We should not cast the big datatype to smaller one. Like from double to float long to integer. TIn these cases there will be chance of loosing the valuable data itself.
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When should a type cast be used?
There are two situations in which to use a type cast. The first use is to change the type of an operand to an arithmetic operation so that the operation will be performed properly. The second case is to cast pointer types to and from void * in order to interface with functions that expect or return void pointers. For example, the following line type casts the return value of the call to malloc()...
kbjarnason
- Jul 2nd, 2010
Very, very, *VERY* rarely. My rule of thumb is, if you see a cast, expect a design error.One classic example of this is the oh-so-popular casting of the return value of malloc. Don't d...
srinivasrao
- Oct 9th, 2007
Type cast should be used in case of if we want to assign a void pointer to a pointer of some data type.eg:void *ptr;int *c;c=(int *)ptr;
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">What is the difference between#include< >and#include" "
kbjarnason
- Jul 2nd, 2010
#include "file.h" tells the preprocessor to look in places other than the standard locations first; generally this means looking in the current directory.#include <file.h> tells the preprocessor to look in the standard locations.
ashutosh_dasgupta
- Apr 29th, 2006
#include <filename>#include "filename"both of which cause a new file to be read at the point where they occur. It's as if the single line containing the directive is replaced by the contents of ...
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What is the draw back in using friend function in c++
kbjarnason
- Jul 2nd, 2010
The basic problem is that it blows away your encapsulation. Friend functions see right through "protected" and "private" and can see blinkin' everything.Or, in other words, "your friends get to play with your private parts." :)
muthu kumar k
- Mar 27th, 2006
check this FAQ listhttp://www.parashift.com/c++-faq-lite/friends.html#faq-14.3
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According to ANSI specifications which is the correct way of declaring main() when it receives command line arguments?
A) main(int argc, char *argv[]) B) main(argc,argv) int argc; char *argv[];C) main() {int argc; char *argv[]; }D) None of the above
kbjarnason
- Jul 2nd, 2010
None of the above. It should be:int main( int argc, char *argv[] )or int main( int argc, char **argv )Note that: a) these are different syntax for the same thing b) relia...
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Write a program to delete itself after execution?
kbjarnason
- Jul 2nd, 2010
There is no reliable way to do this in C.First, if you use the conventional form of main - int main(int argc, char *argv[] ) - then argv[0] is supposed to hold the "program name" - but this ...
umeshknair
- Sep 21st, 2006
include <dos.h>include <stdio.h>int main(int cnt, char **vec){ remove(vec[0]); return 0;}-dot-
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Why does a character constant require two bytes of memory space in C programming
kbjarnason
- Jul 2nd, 2010
They don't.char a; - a is a char variable, which requires one byte's storage.'a' - 'a' is a character constant, which is of type _int_, which requires the same storage as...
abhimanipal
- Jul 15th, 2009
Int main(){ char c='A'; const char a= 'C'; printf("%dn",sizeof(c)); printf("%dn",sizeof(a)); return 0;}The output of this one is11
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What does e stand for in getche() function in C language.
kbjarnason
- Jul 2nd, 2010
It stands for nothing, as C has neither a getch nor a getche function.However, some implementations include a getch and getche function, which are generally intended to get characters from a keyboard,...
Shilpa
- May 19th, 2007
Hi , in getche() e stands for "echo" When the function is encountered, user has to type in any key that it displays on monitor( echos characher). In case of getch() function it accepts character but doesnt display that. Have a fun with CShilpa
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What is the advantage of zero filling in calloc() ?
kbjarnason
- Jul 2nd, 2010
I rarely use calloc; the zero-filling is, for the most part, simply a waste of cycles. In general, you know how much data in stuffed in your buffer, so just read that much back out.However, ther...
ravi_529
- Jan 22nd, 2008
Most of the times you need to zero out the mem by using bzero or memset.U need not do it that way here.And also if it is to be alocated for a string,strlen(allocated array) is automatically 0.Which is a much safer method.
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What is the application of itoa()
kbjarnason
- Jul 2nd, 2010
Since C doesn't define an itoa function, it's application could be anything at all.By contrast, the atoi function is used to convert a string representation of an integer value to an actual in...
shine_babu
- Jul 17th, 2007
Converts an integer value to a null-terminated string using the specified base.If base is 10 and value is negative, the resulting string is preceded with a minus sign (-). With any other base, value is always considered unsigned.
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How can I convert a number to a string?
The standard C library provides several functions for converting numbers of all formats (integers, longs, floats, and so on) to strings and vice versa The following functions can be used to convert integers to strings: Function Name Purpose itoa() Converts an integer value to a string. ltoa() Converts a long integer value to a string. ultoa() Converts an unsigned long integer value to a string....
kbjarnason
- Jul 1st, 2010
Note that while itoa, ltoa and the like may be provided, these are not standard functions. itoa is, but is both unreliable and used for a different purpose.There is no trivial "one size fit...
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Find Number of Occurrences
How will you find the number of occurrences of a particular string in the given input string?
kbjarnason
- Jul 1st, 2010
The question is insufficiently specified. For example: "Find the number of occurrences of NN in the string NNNNN"One answer would be 2 occurrences - the first NN pair, the second...
printfbabu
- Dec 29th, 2009
Int computeSubStrings(const char *string,const char *substr){ int count = 0; char *token = strstr(string,substr); while(token != NULL) { count++; token = strstr(token + 1,substr); } return count;}The above function can be used for counting no. of occurences of a substring in a string
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Does ++p faster than p++?
kbjarnason
- Jul 1st, 2010
The correct answer is that the language does not define the performance of such operations; how they are implemented, how they are optimized and whether one is faster than the other are implementation-specific details, which may very well change, even radically, from one implementation to the next.
sandyseaweed
- Nov 7th, 2008
speed is the same. int iSpeedTest = i++;00413773 mov eax,dword ptr [ebp-0Ch] 00413776 mov dword ptr [ebp-150h],eax 0...
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Memory Allocation
we say stack is allocated to the local variables ,formal arguments and return addresses of a function for manipulating function calls?but the question arises when does the stack allocation to above things take place?at compile time or run time.And by the way what about automatic memory allocation.what is it?
kbjarnason
- Jul 1st, 2010
C neither requires nor defines a stack; at most it requires, in some cases, behaviour which is stack-like, but could be provided by any number of means.As to when the allocation is done, again, this i...
coolquasar
- Sep 15th, 2008
Memory is allocated only during the runtime, and compiler just decides the amount of memory needed by each variable... It just adds the displacement value to be added to the Base Stack pointer for "Local Variables" Allocation.
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A Program that does nothing
Write a program in C that does nothing not even takes memory?
kbjarnason
- Jul 1st, 2010
I suspect it is impossible to write a C program which "takes no memory", unless one rewrites the startup code for the implementation.For example, argv[0] is the "program name", whi...
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