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C string manipulation

Posted on 2003-12-05
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Last Modified: 2010-04-15
Hi,
I am trying to extract a substring from a C string(character array).  Specifically, I am trying to extract the substring up to the first delimiter '|'.
Example: if i have the string 'abcd| efg'
I want to get the C string 'abcd' and return it.
Thanks.
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Question by:aomega
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6 Comments
 
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sunnycoder earned 125 total points
ID: 9886598
char * string = "abcd| efg";
char buffer[10];

temp = strchr ( string, '|' );
strncpy ( buffer, string, temp - string );
buffer[temp - string] = 0;

now buffer has the required string
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by:sunnycoder
ID: 9886602
another alternative is to use strtok

temp = strtok ( string, "|" );
return temp;

beware, strtok will modify your original string unlike strchr
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Author Comment

by:aomega
ID: 9886791
SunnyCoder,
The 5th line : strncpy ( buffer, string, temp - string ) has temp-string as the third parameter.  I am not familiar with subtracting character arrays. What exactly does this accomplish?  thanks.
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LVL 45

Expert Comment

by:sunnycoder
ID: 9886799
it is not subtracting arrays but pointer .. pointers are nothing but addresses (numbers)
e.g.

string starts at 1000

a  1000
b  1001
c   1002
d  1003
|   1004
e  1005
f   1006
g  1007

after strchr string = 1000 and temp = 1004
1004 - 1000 = 4 .. so it will copy 4 chars
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Author Comment

by:aomega
ID: 9886843
thanks for the explanation.
I have pretty much the same as your first example except char *string being passed as a parameter to the function.

char *getKey(char *line){
static char buffer[1000];
char *temp;

temp = strchr(line, '|');
strncpy(buffer, line, temp-line);
buffer[temp-line] = '\0';
return(buffer);
}

I am gettting a segfault at the line strncpy.  I am not quite sure why that is in this case.
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by:sunnycoder
ID: 9886861
runs perfectly
... the segfault may be at some other line ... also you are not performing any error checking ... what if strchr returns NULL ?

#include <stdio.h>
#include <string.h>

char * getkey ( char * a )
{
        static char buffer[100];

        char * temp;

        temp = strchr (a, '|' );

        strncpy ( buffer, a, temp - a );

        buffer [ temp - a ] = 0;

        return buffer;
}

int main ()
{
        char * a = "abcd|efg";

        char * t;

        t = getkey ( a );

        printf ( "%s\n", t );
}
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