Case conversion in C

zaichik · 09-11-2005, 07:40 PM

Hi folks,

Looking for a way to convert string to upper case in C. I have seen references to strupr( ) but it does not work for me.

I am looking for something that works something like this:

Code:

char *myString = "aBc123"
magicFunction( myString );
printf( "Upper case string: %s\n", myString );
//output is Upper case string: ABC123

As always, TIA for any help or links!

Matir · 09-11-2005, 08:11 PM

Code:

#include <ctype.h>
#include <string.h>

char *str="hello world";
int i;

for(i=0;i<strlen(str);i++)
    str[i]=toupper(str[i]);

Wrap it as a function or macro as needed.

zaichik · 09-11-2005, 08:34 PM

Hi,

Thanks for the reply. That seems simple enough, and yet I am getting a segfault when I try to run it. It's in the line that makes the call to toupper, according to gdb. Here is what I have:

Code:

#include <ctype.h>
#include <string.h>

void to_upper( char *the_string );

int main( void ) {

        char *a = "aBc:123";
        to_upper( a );
        printf( "New string: %s\n", a );
        return( 0 );
}

void to_upper( char *the_string ) {

        int x;
        for( x = 0; x < strlen( the_string ); x++ )
                the_string[ x ] = toupper( the_string[ x ] ); // segfault here
        return;
}

Ideas?

deiussum · 09-11-2005, 09:05 PM

Quote:

Originally posted by Matir

Code:

#include <ctype.h> #include <string.h> char *str="hello world"; int i; for(i=0;i<strlen(str);i++) str[i]=toupper(str[i]);

Wrap it as a function or macro as needed.

There's a slight problem with the above code. You are trying to modify memory that is in the read-only data section, which will result in a segfault. (As Zaichik already found....)

The following modified code should work.

Code:

#include <ctype.h>
#include <string.h>

void to_upper( char *the_string );

int main( void ) {

        char a[] = "aBc:123";
        to_upper( a );
        printf( "New string: %s\n", a );
        return( 0 );
}

void to_upper( char *the_string ) {

        int x;
        for( x = 0; x < strlen( the_string ); x++ )
                the_string[ x ] = toupper( the_string[ x ] ); // segfault here
        return;
}

Matir · 09-11-2005, 09:14 PM

Yeah, actually, oddly enough, it seems that char *="VAL"; makes the variable a constant.

Changing it to be: "char a[]=" makes it work.

zaichik · 09-11-2005, 09:14 PM

Hi,

How about this instead?

Code:

#include <ctype.h>
#include <string.h>

void to_upper( char *the_string );

int main( void ) {
        char *a;
        a = ( char * ) malloc( 12 );
        sprintf( a, "aBc:123" );
        to_upper( a );
        printf( "New string: %s\n", a );
        return( 0 );
}
void to_upper( char *the_string ) {

        int x;
        for( x = 0; x < strlen( the_string ); x++ )
                the_string[ x ] = toupper( the_string[ x ] );
        return;
}

That would be in the writable area, yes? And this compiles and runs, but the output is simply
New string:

Matir · 09-11-2005, 09:17 PM

Quote:

Originally posted by zaichik
Hi,

How about this instead?

Code:

#include <ctype.h> #include <string.h> void to_upper( char *the_string ); int main( void ) { char *a; a = ( char * ) malloc( 12 ); sprintf( a, "aBc:123" ); to_upper( a ); printf( "New string: %s\n", a ); return( 0 ); } void to_upper( char *the_string ) { int x; for( x = 0; x < strlen( the_string ); x++ ) the_string[ x ] = toupper( the_string[ x ] ); return; }

That would be in the writable area, yes? And this compiles and runs, but the output is simply
New string:

This code works fine for me.

zaichik · 09-11-2005, 09:32 PM

Hmm.

Thinking I was missing some includes, I added a couple, so now I have:

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

Still, the string is not printing out for me, neither the original nor the modified version.

?

Matir · 09-11-2005, 09:36 PM

Does compiling with -Wall reveal any more warnings? -pedantic?

zaichik · 09-11-2005, 09:40 PM

Nope:

Code:

me@here# gcc -Wall -pedantic -o upper -g to_upper.c
me@here# ./upper
Old string:
New string:
me@here#

(I added a line in main() before the call to to_upper to print the string a after sprintf() ).

I am flummoxed.

Matir · 09-11-2005, 09:43 PM

If you're familiar with gdb, have you tried stepping through it through gdb? What does sprintf return?

zaichik · 09-11-2005, 10:05 PM

Hi David,

gdb showed me that sprintf() wasn't being called at all!

Code:

(gdb) break 1
Breakpoint 1 at 0x80483e4: file to_upper.c, line 1.

(gdb) run
Starting program: /home/justme/upper

Breakpoint 1, main () at to_upper.c:7
7       int main( void ) {
(gdb) step
10              a = ( char * ) malloc( 12 );
(gdb)
11              printf( "Old string: %s\n", a );
(gdb)
Old string:
12              to_upper( a );
(gdb) print a
$1 = 0x9dc5008 ""
(gdb) step

Somehow between copying the code for the earlier post and actually saving and compiling, the sprintf() call was lost entirely! Embarrassing!

Replaced and all is dandy now, thanks for your patience!

Matir · 09-11-2005, 10:18 PM

Lol. Fair enough. I'm glad to meet someone who knows his way around gdb.

zaichik · 09-11-2005, 10:28 PM

Unfortunately, I can't say I know my way around it. I can compile with -g, and know how to set a break point, step, and print. I am sure it can do much more, like setting watches and maybe looking at the stack, but I don't know what. Once this project I am working on is done, I will spend some quality time with the man page for gdb.

Thanks again for your assistance!

Matir · 09-11-2005, 10:31 PM

Debugging core dumps is also helpful. And I'm no gdb power user, but the basics get 90% of the work done anyway.