stdarg

8/7/2019 stdarg

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stdarg

Vijaya Saradhi

8/7/2019 stdarg


In troductio n

So far: ± writte n fun ctio n s with fixed n umber of argume n ts ±

fixed data typespri n tf (sca n f) ca n take variable n umber of argume n ts

Variable data typesCan we write fu n ctio n s which accepts variablen umber of argume n ts?

8/7/2019 stdarg


ExampleFinding minimum of given set of numbers:

int min2( int n1, int n2 )

{

if(n1 < n2 ) return n1;

elsereturn n2;

}

int min3( int n1, int n2, int n3 ){

int n = min2(n1, n2 ) ;return ( min2( n, n3) ) ;

}

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Variable argume n ts?

Can we have a fu n ctio n min that acceptsvariable argume n ts?

Calls to this fu n ctio n looks some thi n g like: ± min (3, 2); ± min (4, 3, 2); ± min (5, 4, 3, 2); ± min (6, 5, 4, 3, 2); ± etc.

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O bservatio n

N umber of argume n ts are u n kn ow n

T heir type is n ot specified before ha n d

How to declare this ki n d of fu n ctio n s?

What is declaratio n of pri n tf/sca n f? ± in t pri n tf(con st char *format, ); ± in t sca n f(con st char *format , );

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stdarg

Has three useful macros ± va_start ±

va_arg ± va_e n d

Help us go through variable argume n ts list

Un

derstan

d type of argumen

tsva_list is a type which holds the i n formatio n to argume n t list

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How to do?

Four steps i n volved

Get a hold of argume n t list ± through va_list

In itialize the argume n t list

walk through the argume n t liste n d the walk

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Example# include<stdio.h># include<stdarg.h>

int main(int argc, char *argv[] )

{

int min(int length, ... ) ;int k = 0;

k = min(2, 3, 2 ) ;k = min(3, 4, 3, 2 ) ;

k = min(4, 5, 4, 3, 2)

;k = min(5, 6, 5, 4, 3, 2 ) ;k = min(6, 7, 6, 5, 4, 3, 2 ) ;k = min(7, 8, 7, 6, 5, 4, 3, 2 ) ;

}

int min(int length, ... )

{

va_list arg_list;int i = 0, min_m = 100000;

va_start (arg_list, length ) ;for( i = 0; i < length; i++ )

{

int n = va_arg (arg_list, int ) ;if( n < min_m )

min_m = n;}va_end (arg_list ) ;return min_m;

}

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M in i prin tf # include<stdio.h># include<stdarg.h>


{

void miniprintf(char *format, ... ) ;int k = 10;double d = 70.7;

miniprintf(³%d%f\n´, k, d ) ;

}

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M in i prin tf Co n td.void miniprintf(char *format, ... )

{

va_list arg_list;int k = 0;double d = 0;char *p = NULL;

va_start (arg_list, format ) ;for( p = format; *p; p++ )

{

if( *p != µ%¶)

{

putchar(*p ) ;continue;

}

switch( *++p )

{

case µd¶:k = va_arg (arg_list, int ) ;printf(³%d\n´, k ) ;break;

case µf¶:d= va_arg (arg_list, double ) ;printf(³%f\n´, d ) ;break;

}}va_end (arg_list ) ;

}

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ctype

Get to k n ow about the classificatio n of charactersT

he followin

g are useful fun

ction

sisdigi t ( in t c ) digi t or not ( 0 to 9 )

isbla n k ( in t c ) space or tab

iscn trl ( i n t c ) co n trol character

isgraph( i n t c ) pri n table characterislower ( i n t c )

isupper ( i n t c )

isspace ( i n t c ) tab, n ew li n e, space etc.

isxdigit ( i n t c ) hexa decimal?

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setjmp

with goto ca n tra n sfer co n trol withi n afun ctio n

to tran

sfer con

trol to differen

t fun

ction

± setjmp ± lon gjmp

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Example

mai n ( ) read_li n e get_word get_cmd

mai n

read_li n e

get_word

get_cmd

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What we wa n t?

mai n

read_li n e

get_word

get_cmd

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Setjmp/lo n gjmp# include<stdio.h># include<setjmp.h>

jmp_buf jump_point;


{

if( setjmp(jump_point) != 0 )

printf(³I am back to main\n´ ) ;else

read_line()

;return 0;}

void read_line( )

{

printf(³I am in read_line\n´ ) ;get_word( ) ;

}

void get_word( )

{

printf(³I am in get_word\n´ ) ;if( 1 )

{

printf(³before longjmp\n´ ) ;longjmp(jump_point, 1);

}}

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stdarg