replace substring

[magix]

Hi,

I have
char* str1 = "d:\temp\data\t est.txt"

I want to replace all the "\" to be "\\", so that

the string will have "d:\\temp\\data \\test.txt"

Can you help ?

Regards,
Magix

[James Dow Allen]

Re: replace substring

On May 26, 2:06 pm, magix <mag...@gmail.c omwrote:

I want to replace all the "\" to be "\\", so that

Try
sed ss\\\\s\\\\\\\\ sg

YMMV

James Dow Allen

[Richard Heathfield]

Re: replace substring

magix said:

Hi,
>
I have
char* str1 = "d:\temp\data\t est.txt"

If you have that, you're in trouble, because \d isn't a valid escape
sequence. \t is, but I don't think you really wanted embedded tabs in that
string, did you?

I want to replace all the "\" to be "\\", so that
>
the string will have "d:\\temp\\data \\test.txt"
>
Can you help ?

char *str1 = "d:\\temp\\data \\test.txt";

If that doesn't fix your problem, you need to clarify what your problem is.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[Martin Ambuhl]

Re: replace substring

magix wrote:

Hi,
>
I have
char* str1 = "d:\temp\data\t est.txt"
>
I want to replace all the "\" to be "\\", so that
>
the string will have "d:\\temp\\data \\test.txt"
>
Can you help ?

The string to which str1 points is a string literal, and you should not
attempt to modify it. String literals are usually not modifiable and in
any case your new string takes more space than the string literal does,
so even if you could modify it, you would overrun the end of it.

You need to allocate an array of sufficient space for the new string
(including the terminating zero-byte) and then something like

/* warning: neither tested nor written to be bulletproof
(or even dart-resistant) */
void replaceslash(ch ar *source, char *target)
{
for (;*source; source++)
{
if (*source = '\\') *target++ = *source;
*target++ = *source;
}
}

Now, the code above simply produces two '\\' when it sees one.
But on almost any system, it makes more sense to replace '\\' with '/'
(even windows and dos have no problem with this), when the above
then becomes
void replaceslash(ch ar *source, char *target)
{
for (;*source; source++)
{
if (*source = '\\') *target++ = '/';
else *target++ = *source; /* notice the else! */
}
}

[Szabolcs Borsanyi]

Re: replace substring

On Mon, May 26, 2008 at 12:29:05AM -0700, James Dow Allen wrote:

On May 26, 2:06 pm, magix <mag...@gmail.c omwrote:

I want to replace all the "\" to be "\\", so that

>
Try
sed ss\\\\s\\\\\\\\ sg

This sed solution seems to be off-topic, but, when applied to the OP's
source, could fix the C problem.

The OP should tell how he got that invalid string literal. If it his
own typing, he should replace the backslashes with pairs of backslashes,
either by hand or using the sed script above. (But it is unlikely to have
sed on a platform with path names containing lot's of backslashes.)

(you=OP)
On the other hand, it is an interesting question, how to replace
valid backslash characters in a string to pairs of backslashes, which can
be relevant, e.g. when writing a source code or passing the string to an
other picky application. If that is the case, you can do this replacement
on the course of copying each character to a separate character array.

Third point is, that it is possible to put a string into a character
array , like char path[]="d:\\path"; This character array cannot hold
more characters than it did originally, but feel free to put a big number
between the square brackets so that you do not have this limitation.
(This point is surely covered by the faq)

Szabolcs

>
YMMV
>
James Dow Allen

[Bartc]

Re: replace substring


"magix" <magix8@gmail.c omwrote in message
news:debb18bd-c54b-4446-b60f-fc675d2e1aa2@p2 5g2000pri.googl egroups.com...

Hi,
>
I have
char* str1 = "d:\temp\data\t est.txt"
>
I want to replace all the "\" to be "\\", so that
>
the string will have "d:\\temp\\data \\test.txt"
>
Can you help ?

If str1 really contains those slashes, then it already represents a valid
Windows filename, if that was the idea.

Doubling up the slashes I think still yields a valid filename, but is
unnecessary.

But if that is initialisation code from a C program, the slashes will be
converted or ignored.

Assuming however you do have such a string and want to double up the
slashes, I tried this somewhat fiddly code. You may want to put str1=str2 at
the end, but is anyway just to give an idea. Note the double \\ characters
here are really single.


/* Duplicate \ characters in a string */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(void)
{
char* str1 = "d:\\temp\\data \\test.txt"; /* old string (in const memory)
*/
char* str2 = NULL; /* new string (to be in heap memory) */
char *p,*q;
char c;
int i,len,slashes;

slashes=0;
len=strlen(str1 );

for (i=0; i<len; ++i) /* Calculate size of new string */
if (str1[i]=='\\')++slashe s;

str2=malloc(len +slashes+1);

if (str2!=NULL) {
p=str1;
q=str2;
while (c=*p++) {
*q++ = c;
if (c=='\\') *q++ = '\\';
};
*q++ = 0;
printf("STR1 = %s\n",str1);
printf("STR2 = %s\n",str2);

// free(str2);
}
else
puts("No memory");

}

[Keith Thompson]

Re: replace substring

magix <magix8@gmail.c omwrites:

I have
char* str1 = "d:\temp\data\t est.txt"
>
I want to replace all the "\" to be "\\", so that
>
the string will have "d:\\temp\\data \\test.txt"
>
Can you help ?

You're going to need to be clearer about what you have and what you
want.

Do you mean that you have a declaration:

const char* str1 = "d:\temp\data\t est.txt";

(note: I added the "const" and the semicolon) *in a C source file*,
and you want to modify the C source file so the declaration is

const char* str1 = "d:\\temp\\data \\test.txt";

? If so, I'd say the best tool for the job is a text editor; just add
the extra backslashes and save the file. But that's so trivial that I
suspect it's not really what you were asking.

If you want to modify a large number of such incorrect declarations,
it's going to be difficult. For one thing, backslashes can appear
legitimately in string literals; you wouldn't want to change
"hello, world\n"
to
"hello, world\\n"
.. I can imagine ways to detect which string literals should be
translated and which should be left alone, but it can't be done 100%
reliably, and I wouldn't even make the attempt without a lot more
information.

If you mean that you want to leave the declaration alone and change
the value of the string at run time, you're pretty much out of luck
(and fixing the declaration is a much better idea anyway).

Tell us what you're really trying to do, and we can probably help.

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[CBFalconer]

Re: replace substring

magix wrote:

>
I have
char* str1 = "d:\temp\data\t est.txt"
>
I want to replace all the "\" to be "\\", so that
the string will have "d:\\temp\\data \\test.txt"
>
Can you help ?

No. str1 is a non-writable string. You can create str2 and copy
str1, with modifications, into it. The copy part will look
something like:

while (*p1) {
if ('\' == (*p2++ = *p1++)) *p2++ = '\';
}

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.

** Posted from http://www.teranews.com **

[Antoninus Twink]

Re: replace substring

On 26 May 2008 at 7:32, CBFalconer wrote:

The copy part will look something like:
>
while (*p1) {
if ('\' == (*p2++ = *p1++)) *p2++ = '\';
}

It won't look like that if you want it to pass a code review in any
professional environment. Blech.

[Richard]

Re: replace substring

CBFalconer <cbfalconer@yah oo.comwrites:

magix wrote:

>>
>I have
> char* str1 = "d:\temp\data\t est.txt"
>>
>I want to replace all the "\" to be "\\", so that
>the string will have "d:\\temp\\data \\test.txt"
>>
>Can you help ?

>
No. str1 is a non-writable string. You can create str2 and copy
str1, with modifications, into it. The copy part will look
something like:
>
while (*p1) {
if ('\' == (*p2++ = *p1++)) *p2++ = '\';
}

Note to magix : never, ever lay your code out like this or it will be
laughed out of any code review. Multiple statements on line might save a
little bit vertical real estate but are a pain in the behind to debug
and read. Others might disagree. Only you can decide.

Something like (not compiled or tested but you get the meaning I hope)

char c;
while (c = *d++ = *s++) { /* s==source, d==destination */
if (c=='\')
*d++ = '\';
}

[Ben Bacarisse]

Re: replace substring

Richard<rgrdev@ gmail.comwrites :

CBFalconer <cbfalconer@yah oo.comwrites:
>

>magix wrote:

<a question about doubling \s>

>>Can you help ?

<snip>

> while (*p1) {
> if ('\' == (*p2++ = *p1++)) *p2++ = '\';
> }

>
Note to magix : never, ever lay your code out like this or it will be
laughed out of any code review. Multiple statements on line might save a
little bit vertical real estate but are a pain in the behind to debug
and read. Others might disagree. Only you can decide.
>
Something like (not compiled or tested but you get the meaning I hope)
>
char c;
while (c = *d++ = *s++) { /* s==source, d==destination */
if (c=='\')
*d++ = '\';
}

The layout is up to you, of course, but you've altered the semantics.

--
Ben.

[Richard Harter]

Re: replace substring

On Fri, 30 May 2008 16:48:42 +0200, Richard<rgrdev@ gmail.com>
wrote:

>CBFalconer <cbfalconer@yah oo.comwrites:
>

>magix wrote:

>>>
>>I have
>> char* str1 = "d:\temp\data\t est.txt"
>>>
>>I want to replace all the "\" to be "\\", so that
>>the string will have "d:\\temp\\data \\test.txt"
>>>
>>Can you help ?

>>
>No. str1 is a non-writable string. You can create str2 and copy
>str1, with modifications, into it. The copy part will look
>something like:
>>
> while (*p1) {
> if ('\' == (*p2++ = *p1++)) *p2++ = '\';
> }

>
>Note to magix : never, ever lay your code out like this or it will be
>laughed out of any code review. Multiple statements on line might save a
>little bit vertical real estate but are a pain in the behind to debug
>and read. Others might disagree. Only you can decide.
>
>Something like (not compiled or tested but you get the meaning I hope)
>
char c;
while (c = *d++ = *s++) { /* s==source, d==destination */
if (c=='\')
*d++ = '\';
}
>

Obscene noises and horselaughs. I doubt that I would
intentionally hire anyone who objected to CFB's code, which uses
standard C idioms. More strongly, in my opinion anyone who has
difficulty reading it or debugging probably has made a bad career
choice.

Note that CFB's code does not have multiple statements on one
line.

Also I do not like your suggested alternative. Let me count the
ways. YMMV of course.

Introducing c is problematic. In C89 it will need to be at the
beginning of the block in which the loop is contained breaking
the connection between the declaration and the code that uses it.
More importantly it is a bit of obfuscation.

I don't like the multiple assignment trick (c = *d++ = *s++).
Count that as a personal prejudice.

The lines

if (c=='\')
*d++ = '\';

are a definite style error. Either write

if (c=='\') *d++ = '\';

making it clear that the if controls a single statement, or

if (c=='\') {
*d++ = '\';
}

The trouble with the format that you used is that it is fragile;
it is easy to erroneously add another statement to what appears
to be a block. If you do, the code compiles and the error can be
surprisingly hard to find.









Richard Harter, cri@tiac.net
http://home.tiac.net/~cri, http://www.varinoma.com
Save the Earth now!!
It's the only planet with chocolate.

[Keith Thompson]

Re: replace substring

CBFalconer <cbfalconer@yah oo.comwrites:

magix wrote:

>>
>I have
> char* str1 = "d:\temp\data\t est.txt"
>>
>I want to replace all the "\" to be "\\", so that
>the string will have "d:\\temp\\data \\test.txt"
>>
>Can you help ?

>
No. str1 is a non-writable string. You can create str2 and copy
str1, with modifications, into it. The copy part will look
something like:
>
while (*p1) {
if ('\' == (*p2++ = *p1++)) *p2++ = '\';
}

Note that '\' is a syntax error. It should be '\\'.

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Keith Thompson]

Re: replace substring

cri@tiac.net (Richard Harter) writes:

On Fri, 30 May 2008 16:48:42 +0200, Richard<rgrdev@ gmail.com>
wrote:
>

>>CBFalconer <cbfalconer@yah oo.comwrites:

[...]

>> while (*p1) {
>> if ('\' == (*p2++ = *p1++)) *p2++ = '\';
>> }

>>
>>Note to magix : never, ever lay your code out like this or it will be
>>laughed out of any code review. Multiple statements on line might save a
>>little bit vertical real estate but are a pain in the behind to debug
>>and read. Others might disagree. Only you can decide.

[...]

Note that CFB's code does not have multiple statements on one
line.

Yes, it does. It just happens that one of the statements is part of
the other statement.

(Assuming, of course, that '\' is changed to '\\'.)

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[rio]

Re: replace substring


"CBFalconer " <cbfalconer@yah oo.comha scritto nel messaggio
news:483A677F.9 50DC227@yahoo.c om...

magix wrote:

>>
>I have
> char* str1 = "d:\temp\data\t est.txt"
>>
>I want to replace all the "\" to be "\\", so that
>the string will have "d:\\temp\\data \\test.txt"
>>
>Can you help ?

>
No. str1 is a non-writable string. You can create str2 and copy
str1, with modifications, into it. The copy part will look
something like:

while (*p1) {
if ('\' == (*p2++ = *p1++)) *p2++ = '\';
}

here there should be
*p2=0;

so "if ('\' == (*p2++ = *p1++)) *p2++ = '\';"
should be
c=*p2 = *p1; ++p1; ++p2;
if(c=='\') *p2++ = '\';