10-31-2006
override the function in C
hi ,
greetings ,
I have one doubt reg the C functions .
I have a program sample.c , in which i have function name scanf , which reads a a variable and prints the variable inside the function .
this scanf is nothing to do with C library function scanf , but i would like to use only user defined c function scanf .
when it is compiling , it is throwing error indicating scanf args not matching becos compile checks for stdio.h header file for syntax of scanf .
To put in a simple statement , i would like to override a system function and make my c program to take function which i wrote which has same name .
It can be a similar concept of function overloading in C .
For example :
in case macros i can overide any macro inside my program just by doing #undef name
#define name "unix"
it works for macros ,
in same line how to override the function?
Many Thanks in advance !
Thanks
Naren
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scanf(3int) scanf(3int)
Name
scanf, fscanf, sscanf - convert formatted input
Syntax
#include <stdio.h>
int scanf( format [, pointer ] ... )
char *format;
int fscanf( stream, format [, pointer ] ... )
FILE *stream;
char *format;
int sscanf( s, format [, pointer ] ... )
char *s, *format;
Description
The international functions and are similar to the standard I/O functions. The difference is that the international functions allow you to
use the %digit$ conversion character in place of the I% character you use in the standard I/O functions. The digit is a decimal digit n
from 1 to 9. The international functions apply conversions to the n th argument in the argument list, rather than to the next unused argu-
ment.
You can use % conversion character in the international functions. However, you cannot mix the % conversion character with the %digit$
conversion character in a single call.
In all cases, uses the radix character and collating sequence that is defined by the last successful call to category or If the radix or
collating sequence is undefined, the function uses the C locale definitions.
International Environment
LC_COLLATE Contains the user requirements for language, territory, and codeset for the character collation format. affects the behav-
ior of regular expressions and the string collation functions in If is not defined in the current environment, provides the
necessary default.
LC_NUMERIC If this environment is set and valid, uses the international language database named in the definition to determine radix
character rules.
LANG If this environment variable is set and valid uses the international language database named in the definition to determine
collation and character classification rules. If or is defined, their definitions supersede the definition of LANG.
Examples
The following shows an example of using the function:
scanf("%2$s %1$d", integer, string)
If the input is `` january 9 '', the function assigns 9 to and ``january'' to
Return Values
The function returns the number of successfully matched and assigned input fields. This number can be zero if the function encounters
invalid input characters, as specified by the conversion specification, before it can assign input characters.
If the input ends before the first conflict or conversion, returns EOF. These functions return EOF on end of input and a short count for
missing or invalid data items.
Environment
In POSIX mode, the E, F, and X formats are treated the same as the e, f, and x formats, respectively; otherwise, the upper-case formats
expect double, double, and long arguments, respectively.
See Also
intro(3int), setlocale(3), strtod(3), strtol(3), printf(3int), getc(3s), printf(3s), scanf(3s)
Guide to Developing International Software
scanf(3int)