C Language, please help newbie string replacement in big file

nur e
#1 / 17

please help newbie string replacement in big file

I am doing some string manipulation on a file:

the file has all sorts of characters strings, including whiteline i.e
content, part of the file - video.reg is as follows:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Hardware
Profiles\Current\System\CurrentControlSet\SERVICES\ATIRAGE3]

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Hardware
Profiles\Current\System\CurrentControlSet\SERVICES\ATIRAGE3\DEVICE0]

"DefaultSettings.YResolution"=dword:00000258
"DefaultSettings.VRefresh"=dword:0000004b
"DefaultSettings.Flags"=dword:00000000
"DefaultSettings.XPanning"=dword:00000000
"DefaultSettings.YPanning"=dword:00000000

The problem is i want to replace the occurance of
"DefaultSettings.VRefresh"=dword:0000004b with
"DefaultSettings.VRefresh"=dword:0000004C and save the changes to the
same file or different file

This is the code i have written so far but doesnt work
It produces an empty file

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

static occur = 0;
int main(void)
{

FILE *fp, *tmp;

if ((fp=fopen("C:\\video.reg","r"))==NULL){
/* error */
}

if ((tmp=fopen("C:\\videob.reg","w+"))==NULL){
/* error */
printf("error videob");

}

else{

char line[256];

while( ! feof(fp) ) {
fgets(line, sizeof(line), fp);

{
char *ptr;
while ((ptr = strstr (line,
"\"DefaultSettings.VRefresh\"=dword:0000004b")) != NULL) {
strcpy (ptr,
"DefaultSettings.VRefresh\"=dword:0000004c");
}
}

fputs(ptr, tmp);
}

}

return 0;

fclose(tmp);

fclose(fp);

This doesnt work, it produces an empty file!!

Thank you all in advance..

nur

Sun, 13 Mar 2005 23:33:51 GMT

Emmanuel Delahay
#2 / 17

please help newbie string replacement in big file

Quote:

> I am doing some string manipulation on a file:

> the file has all sorts of characters strings, including whiteline i.e
> content, part of the file - video.reg is as follows:

> [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Hardware
> Profiles\Current\System\CurrentControlSet\SERVICES\ATIRAGE3]

> [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Hardware
> Profiles\Current\System\CurrentControlSet\SERVICES\ATIRAGE3\DEVICE0]

> "DefaultSettings.YResolution"=dword:00000258
> "DefaultSettings.VRefresh"=dword:0000004b
> "DefaultSettings.Flags"=dword:00000000
> "DefaultSettings.XPanning"=dword:00000000
> "DefaultSettings.YPanning"=dword:00000000

> The problem is i want to replace the occurance of
> "DefaultSettings.VRefresh"=dword:0000004b with
> "DefaultSettings.VRefresh"=dword:0000004C and save the changes to the
> same file or different file

This is a job for any decent text editor. Try UltraEdit. It's a must!

http://www.ultraedit.com/

- Show quoted text -

Quote:

> This is the code i have written so far but doesnt work
> It produces an empty file

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

> static occur = 0;
> int main(void)
> {

> FILE *fp, *tmp;

> if ((fp=fopen("C:\\video.reg","r"))==NULL){
> /* error */
> }

> if ((tmp=fopen("C:\\videob.reg","w+"))==NULL){
> /* error */
> printf("error videob");

> }

You open the same file twice? This is not portable and dangerous. The good
way is to use 2 different files. I hope your error handling stops the
execution...

Quote:

> else{

> char line[256];

> while( ! feof(fp) ) {

(FAQ) C is not Pascal. This is not the good way to find the end of a file.
You must read your manual and test the value returned by the
reading function (here fgets()).

Quote:

> fgets(line, sizeof(line), fp);

> {
> char *ptr;
> while ((ptr = strstr (line,
> "\"DefaultSettings.VRefresh\"=dword:0000004b")) != NULL) {

Doesn't work because fgets() gets the '\n' too.

Quote:

> strcpy (ptr,
> "DefaultSettings.VRefresh\"=dword:0000004c");
> }
> }

> fputs(ptr, tmp);

You forgot the final '\n'

Quote:

> }

> return 0;

> fclose(tmp);

> fclose(fp);

--
-ed- emdel at noos.fr ~]=[o
FAQ de f.c.l.c : http://www.isty-info.uvsq.fr/~rumeau/fclc/
C-library: http://www.dinkumware.com/htm_cl/index.html
"Mal nommer les choses c'est ajouter du malheur au monde."
-- Albert Camus.

Mon, 14 Mar 2005 01:36:12 GMT

Ryan Henness
#3 / 17

please help newbie string replacement in big file

<snip>

Quote:

> > FILE *fp, *tmp;

> > if ((fp=fopen("C:\\video.reg","r"))==NULL){
> > /* error */
> > }

> > if ((tmp=fopen("C:\\videob.reg","w+"))==NULL){
> > /* error */
> > printf("error videob");

> > }

> You open the same file twice? This is not portable and dangerous. The good
> way is to use 2 different files. I hope your error handling stops the
> execution...

Uh, look again. Carefully.

Ryan.

Mon, 14 Mar 2005 01:33:13 GMT

Eric Sosma
#4 / 17

please help newbie string replacement in big file

Quote:

> I am doing some string manipulation on a file
> [that resembles a text version of a Windows registry]

> This is the code i have written so far but doesnt work
> It produces an empty file [...]

I'm not entirely sure why you wind up with an empty file,
but one possible explanation is that the input "c:\\video.reg"
file might not have the format you expect. <off-topic> The
Windows registry files themselves use a proprietary binary
format which needs to be translated to (and from) the textual
representation you've shown. If you're trying to read an
untranslated binary registry file and treat it as text, all
manner of odd things might happen. </off-topic>

In case that's not the problem, let me point out a few
miscellaneous errors and oddities in your program. I don't
see how any of them would explain the empty output file, but
cleaning away extraneous bugs may help you locate the Big One:

Quote:

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

You don't use any of the facilities in <stdlib.h>, so you
needn't #include it. The inclusion is harmless, though.

Quote:

> static occur = 0;

You don't use this variable anywhere, so there's no point
in defining it. The definition is harmless, though.

Quote:

> int main(void)
> {

> FILE *fp, *tmp;

> if ((fp=fopen("C:\\video.reg","r"))==NULL){
> /* error */
> }

If this fopen() fails you'll be in big trouble, because you
just plow straight ahead as if all had gone well. Later when
you try to use the NULL-valued `fp', bad things will almost
certainly happen.

Quote:

> if ((tmp=fopen("C:\\videob.reg","w+"))==NULL){
> /* error */
> printf("error videob");

> }

> else{

> char line[256];

> while( ! feof(fp) ) {

This is the wrong way to use feof(), and will give you
erroneous results. See Question 12.2 in the comp.lang.c
Frequently Asked Questions (FAQ) list

http://www.*-*-*.com/ ~scs/C-faq/top.html

Quote:

> fgets(line, sizeof(line), fp);

> {
> char *ptr;
> while ((ptr = strstr (line,
> "\"DefaultSettings.VRefresh\"=dword:0000004b")) != NULL) {
> strcpy (ptr,
> "DefaultSettings.VRefresh\"=dword:0000004c");
> }

There are at least four weird things here. First, the
use of `while' is distinctly peculiar: a simple `if' would
seem more appropriate. Second, using strstr() instead of
strcmp() might be defensible on the grounds that it could
locate the target string in the middle of other stuff, but
since the strcpy() will obliterate any trailing characters
it doesn't seem you've really thought this through. Third,
one of the obliterated characters will be the '\n' that marks
the end of the line; the result will be that the "...004c"
will {*filter*}right up against the characters from the next
line rather than appearing at the end of their own line. And
finally, the replacement string lacks an initial double-quote.

Quote:

> }

> fputs(ptr, tmp);
> }

> }

> return 0;

By returning zero unconditionally, the program always
indicates "success" even when it's detected and reported a
failure to open "c:\\videob.reg". That's not fatal -- you're
at liberty to write a program that always "succeeds" no matter
how much trouble it gets into -- but it's unusual.

Quote:

> fclose(tmp);

> fclose(fp);

Because of the `return' statement above, these two fclose()
calls will never be executed. Again, that's not necessarily
fatal: the ordinary actions of program termination will, among
other things, close all still-open streams. Still, the presence
of these unreachable calls suggests you've overlooked something.

--

Mon, 14 Mar 2005 01:49:42 GMT

ak
#5 / 17

please help newbie string replacement in big file

|I am doing some string manipulation on a file:
|
|the file has all sorts of characters strings, including whiteline i.e
|content, part of the file - video.reg is as follows:
|
|[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Hardware
|Profiles\Current\System\CurrentControlSet\SERVICES\ATIRAGE3]
|
|[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Hardware
|Profiles\Current\System\CurrentControlSet\SERVICES\ATIRAGE3\DEVICE0]
|
|"DefaultSettings.YResolution"=dword:00000258
|"DefaultSettings.VRefresh"=dword:0000004b
|"DefaultSettings.Flags"=dword:00000000
|"DefaultSettings.XPanning"=dword:00000000
|"DefaultSettings.YPanning"=dword:00000000
|
|The problem is i want to replace the occurance of
|"DefaultSettings.VRefresh"=dword:0000004b with
|"DefaultSettings.VRefresh"=dword:0000004C and save the changes to the
|same file or different file
|
|This is the code i have written so far but doesnt work
|It produces an empty file
|
|#include <stdio.h>
|#include <string.h>
|#include <stdlib.h>
|
|static occur = 0;
|int main(void)
|{
|
|
|
|
|FILE *fp, *tmp;
|
|if ((fp=fopen("C:\\video.reg","r"))==NULL){
| /* error */
| }
|
|
|if ((tmp=fopen("C:\\videob.reg","w+"))==NULL){
| /* error */
| printf("error videob");
|
| }
|
|else{
|
|
| char line[256];
|
| while( ! feof(fp) ) {
| fgets(line, sizeof(line), fp);
|
| {
| char *ptr;
| while ((ptr = strstr (line,
|"\"DefaultSettings.VRefresh\"=dword:0000004b")) != NULL) {
| strcpy (ptr,
|"DefaultSettings.VRefresh\"=dword:0000004c");
| }
| }
|
| fputs(ptr, tmp);
| }
|
|
| |
| return 0;
|
|
|fclose(tmp);
|
|fclose(fp);
|
|
|This doesnt work, it produces an empty file!!
|
|Thank you all in advance..
|
|nur

try for instance:

static char keyword[] = "\"DefaultSettings.VRefresh\"=dword:0000004";
static char replace[] = "\"DefaultSettings.VRefresh\"=dword:0000004c";

while (fgets( line, sizeof(line), fp)!=NULL) {
if (!strnicmp( line,keyword, strlen( keyword) ) {
strcpy(line,replace);
}
fputs(line,tmp);

Quote:

}

not checked for syntax.
hth/ak

Mon, 14 Mar 2005 02:22:53 GMT

Emmanuel Delahay
#6 / 17

please help newbie string replacement in big file

Quote:

>> > FILE *fp, *tmp;

>> > if ((fp=fopen("C:\\video.reg","r"))==NULL){
>> > /* error */
>> > }

>> > if ((tmp=fopen("C:\\videob.reg","w+"))==NULL){
>> > /* error */
>> > printf("error videob");

>> > }

>> You open the same file twice? This is not portable and dangerous. The
>> good way is to use 2 different files. I hope your error handling
>> stops the execution...

> Uh, look again. Carefully.

Oops. T'was so a small difference! My apologies to the OP.

--
-ed- emdel at noos.fr ~]=[o
FAQ de f.c.l.c : http://www.isty-info.uvsq.fr/~rumeau/fclc/
C-library: http://www.dinkumware.com/htm_cl/index.html
"Mal nommer les choses c'est ajouter du malheur au monde."
-- Albert Camus.

Mon, 14 Mar 2005 02:48:49 GMT

Emmanuel Delahay
#7 / 17

please help newbie string replacement in big file

Quote:

> static char keyword[] = "\"DefaultSettings.VRefresh\"=dword:0000004";
> static char replace[] = "\"DefaultSettings.VRefresh\"=dword:0000004c";

> while (fgets( line, sizeof(line), fp)!=NULL) {
> if (!strnicmp( line,keyword, strlen( keyword) ) {

strnicmp() is not a standard C function. strncmp() should work here.

--
-ed- emdel at noos.fr ~]=[o
FAQ de f.c.l.c : http://www.isty-info.uvsq.fr/~rumeau/fclc/
C-library: http://www.dinkumware.com/htm_cl/index.html
"Mal nommer les choses c'est ajouter du malheur au monde."
-- Albert Camus.

Mon, 14 Mar 2005 02:52:43 GMT

Eric Sosma
#8 / 17

please help newbie string replacement in big file

Quote:

> > I am doing some string manipulation on a file
> > [that resembles a text version of a Windows registry]

> > This is the code i have written so far but doesnt work
> > It produces an empty file [...]

Something I seem to have missed on my first look at your
code is that -- well it ISN'T the code! The stuff you posted
won't compile, much less "produce an empty file." Specifically,
the identifier `ptr' is undefined when it appears in the
`fputs(ptr, tmp);' line:

Quote:

> {
> char *ptr;
> while ((ptr = strstr (line,
> "\"DefaultSettings.VRefresh\"=dword:0000004b")) != NULL) {
> strcpy (ptr,
> "DefaultSettings.VRefresh\"=dword:0000004c");
> }
> }

> fputs(ptr, tmp);

... and there's no other variable named `ptr' lying around
anywhere.

Please, please, please, Only One (and anyone else): if
you want help debugging some code, exhibit THE ACTUAL CODE
and not some kind of paraphrase. If your car is giving you
trouble, do you ask the mechanic to look at your bicycle?

--

Mon, 14 Mar 2005 02:31:47 GMT

nrk
#9 / 17

please help newbie string replacement in big file

Quote:

> I am doing some string manipulation on a file:

> the file has all sorts of characters strings, including whiteline i.e
> content, part of the file - video.reg is as follows:

> [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Hardware
> Profiles\Current\System\CurrentControlSet\SERVICES\ATIRAGE3]

> [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Hardware
> Profiles\Current\System\CurrentControlSet\SERVICES\ATIRAGE3\DEVICE0]

> "DefaultSettings.YResolution"=dword:00000258
> "DefaultSettings.VRefresh"=dword:0000004b
> "DefaultSettings.Flags"=dword:00000000
> "DefaultSettings.XPanning"=dword:00000000
> "DefaultSettings.YPanning"=dword:00000000

> The problem is i want to replace the occurance of
> "DefaultSettings.VRefresh"=dword:0000004b with
> "DefaultSettings.VRefresh"=dword:0000004C and save the changes to the
> same file or different file

The first question is: Why not use a decent text editor to do the job (as
your file seems to be text)?

Quote:

> This is the code i have written so far but doesnt work
> It produces an empty file

As Eric mentions, the code won't even compile. Nevertheless, even making
assumptions for it to compile, it is more than likely that you will end up
invoking undefined behavior. Read on.

Quote:

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

> static occur = 0;
> int main(void)
> {

Do you like empty lines? In code, it usually makes your task of finding what
you want more difficult.

Quote:

> FILE *fp, *tmp;

> if ((fp=fopen("C:\\video.reg","r"))==NULL){
> /* error */
> }

Using consistent and readable indentation standards is the first step towards
writing maintainable, better programs.

Quote:

> if ((tmp=fopen("C:\\videob.reg","w+"))==NULL){
> /* error */
> printf("error videob");

> }

The above should have been an else if. Otherwise, even when the first fopen
fails, you could still enter the else part below with a NULL file pointer to
read from and that would invoke undefined behavior. So, something along the
lines of:
if ( (fp = fopen(source_name)) == NULL ) {
/* error */
}
else {
if ( (tmp = fopen(dest_name)) == NULL ) {
/* error */
}
else {
/* do our processing */
}
}

Quote:

> else{

> char line[256];

> while( ! feof(fp) ) {
> fgets(line, sizeof(line), fp);

Bad idea. When using fgets, you should always check its return to see if EOF
or an I/O error has occurred. So, what you want is:
while ( fgets(line, sizeof(line), fp) != NULL ) {

Quote:

> {

Why start a new block here? It doesn't seem to serve any useful purpose.

Quote:

> char *ptr;

I will assume that the declaration of ptr is made outside this block.

Quote:

> while ((ptr = strstr (line,
> "\"DefaultSettings.VRefresh\"=dword:0000004b")) != NULL) {

Read the documentation of strstr. It returns NULL if there was no match for
the needle in the haystack. In which case, what happens to the fputs that
uses ptr down below? Undefined behavior.

Quote:

> strcpy (ptr,
> "DefaultSettings.VRefresh\"=dword:0000004c");

If your intent was to replace the occurrences of the original string with the
target string, this is not the way to do it. What strcpy will do is that it
will truncate your input line at the end of the first occurrence of the search
string. For e.g.
If input line was:
"I am a big \"DefaultSettings.VRefresh\"=dword:0000004b line\n"
Your strcpy will convert it to:
"I am a big \"DefaultSettings.VRefresh\"=dword:0000004c"

Since your search and replacement strings are the same size (assuming you
missed out a \" in the replacement string), you could take the following approach:

const char replstr[] = "\"DefaultSettings.VRefresh\"=dword:0000004c";

and inside the while loop:
int replindex;
for ( replindex = 0; replindex < sizeof(replstr)-1; ++replindex )
*ptr++ = replstr[replindex];

Or in your case where only the last character is to be changed:
ptr[sizeof(replstr)-1] = replstr[sizeof(replstr)-1];

Quote:

> }
> }

> fputs(ptr, tmp);

You want this to be:
fputs(line, tmp);
and it should be outside the while( (ptr = strstr...) ) loop if you want all
the lines of the input file to be present in your output file as well. In
your strstr loop, ptr would point to some memory inside the array line. So
any changes you make to the contents of ptr in that loop actually changes the
contents of line. So using line in the fputs would give you the new changed
line in the output file.

Quote:

> }

> return 0;

> fclose(tmp);

> fclose(fp);

Huh?? Do you expect these two fclose statements to ever get executed?

HTH,
nrk.

Mon, 14 Mar 2005 08:19:21 GMT

m
#10 / 17

please help newbie string replacement in big file

Quote:

> > This is the code i have written so far but doesnt work
> > It produces an empty file

> > fgets(line, sizeof(line), fp);

> > {
> > char *ptr;
> > while ((ptr = strstr (line,
> > "\"DefaultSettings.VRefresh\"=dword:0000004b")) != NULL) {

> Doesn't work because fgets() gets the '\n' too.

AFAICS, the '\n' read by fgets() into line is irrelevant here...
He's using strstr(), not strcmp(), and so the function will succeed
if the string "\"DefaultSettings.VRefresh\"=dword:0000004b" is in the
line array.

Quote:

> > strcpy (ptr,
> > "DefaultSettings.VRefresh\"=dword:0000004c");
> > }
> > }

> > fputs(ptr, tmp);

This line is his most blatant problem. The code above is mangled,
but as far as I can see, the strcpy() is ONLY called if the previous
strstr() function succeeds. Moreover, ptr is declared in a block which
ends just before fputs, making ptr local to that block and thus meaning
that ptr's storage should be destroyed at the end of the block, before
the call to fputs. Finally, if the strstr() fails, ptr will be NULL
and the call to fputs will invoke undefined behavior.

Matt

Mon, 14 Mar 2005 09:39:53 GMT

nur e
#11 / 17

please help newbie string replacement in big file

Thank you all,

Eric you right about .reg format i had to pipe the resulting .reg to
txt i.e type video.reg > vga.txt

This allowed me to do string manipulation.

Thanks to Rex of team OR,

this is the modified and working code.....

#include <stdio.h>
#include <errno.h> /* for strerror() */
#include <string.h>
#include <stdlib.h>

static occur = 0;
int main(void)
{

FILE *fp, *tmp;

if ((fp=fopen("C:\\video.reg","r"))==NULL){
/* error */

Quote:

}

if ((tmp=fopen("C:\\videob.reg","w+"))==NULL){
/* error */
printf("error videob");

Quote:

}

else{

char line[256];

while( ! feof(fp) ) {
fgets(line, sizeof(line), fp);

{
char *ptr;
while ((ptr = strstr (line,
"\"DefaultSettings.VRefresh\"=dword:0000004b")) != NULL) {
strcpy (ptr, "DefaultSettings.VRefresh\"=dword:0000004c");

Quote:

}
}

fputs(ptr, tmp);

Quote:

}
}

return 0;

fclose(tmp);

fclose(fp);

Mon, 14 Mar 2005 22:38:56 GMT

Eric Sosma
#12 / 17

please help newbie string replacement in big file

Quote:

> Thank you all,

> Eric you right about .reg format i had to pipe the resulting .reg to
> txt i.e type video.reg > vga.txt

> This allowed me to do string manipulation.

> Thanks to Rex of team OR,

> this is the modified and working code.....

No, it isn't. You're lying, and wasting everyone's time.

--

Tue, 15 Mar 2005 00:30:01 GMT

nur e
#13 / 17

please help newbie string replacement in big file

Quote:

> No, it isn't. You're lying, and wasting everyone's time.

Have you tried compiling using DJGPP and on windows 2000 professional???

Guess not?

I have replaced the string "\Def....000.." with "0000004b".

I have compiled this and it did work!! Honest..

Eric how else do you want me to prove it??????

I am ever thankful... Again i want to thank you for your contribution..

Thank you all

Tue, 15 Mar 2005 22:55:32 GMT

ak
#14 / 17

please help newbie string replacement in big file

|> static char keyword[] = "\"DefaultSettings.VRefresh\"=dword:0000004";
|> static char replace[] = "\"DefaultSettings.VRefresh\"=dword:0000004c";
|>
|> while (fgets( line, sizeof(line), fp)!=NULL) {
|> if (!strnicmp( line,keyword, strlen( keyword) ) {
|
|strnicmp() is not a standard C function. strncmp() should work here.

yes, me bad :)

Tue, 15 Mar 2005 23:43:21 GMT

Eric Sosma
#15 / 17

please help newbie string replacement in big file

Quote:

> > No, it isn't. You're lying, and wasting everyone's time.

> Have you tried compiling using DJGPP and on windows 2000 professional???

> Guess not?

I don't have Windows 2000, but I do have DJGPP. When I
run your code through it (default options), the compiler complains

nurein.c: In function `main':
nurein.c:42: `ptr' undeclared (first use in this function)
nurein.c:42: (Each undeclared identifier is reported only once
nurein.c:42: for each function it appears in.)
nurein.c:54: parse error at end of input

Conclusion: You may indeed have gotten the program to work,
but the program wasn't generated from the code you posted.

--

Wed, 16 Mar 2005 00:00:01 GMT