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STL: Replacing consecutive matching elements in a string

 
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lotusny78@yahoo.com
Guest
PostPosted: Fri Apr 15, 2005 7:27 am    Post subject: STL: Replacing consecutive matching elements in a string Reply with quote


Hi everyone,

I'm trying to use the STL to replace every time there are consecutive
tabs with ' ' in a string. I came up with something that works, but it
seems like there should be an easier way to do it. I'm looking for
another strategy, not really bug-fixes as this is semi-spaghetti code.
Also, I don't want to exploit the possibility of string iterators being
pointers. Thanx.
- Sean

class ConsecutiveTabs {
public:
bool operator() (char c1, char c2)
{
if('t' == c1 && 't' == c2)
return true;
else
return false;
}
};

string line;
....
string::iterator beginIt;
while(line.end() !=
(beginIt=
adjacent_find(line.begin(), line.end(), ConsecutiveTabs))) {
if(*beginIt == 't') {
string::iterator endIt = beginIt;
advance(endIt, 2);
line.replace(beginIt, endIt, 1, ' ');
}
}


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simont
Guest
PostPosted: Sat Apr 16, 2005 12:05 am    Post subject: Re: STL: Replacing consecutive matching elements in a string Reply with quote


[email]lotusny78 (AT) yahoo (DOT) com[/email] wrote:
Quote:
Hi everyone,

I'm trying to use the STL to replace every time there are
consecutive tabs with ' ' in a string. I came up with something
that works, but it seems like there should be an easier way to do
it. I'm looking for another strategy, not really bug-fixes as this
is semi-spaghetti code. Also, I don't want to exploit the
possibility of string iterators being pointers. Thanx.
- Sean

Perhaps something like
boost::algorithm::replace_all( str, "tt", " " );

I haven't tried this btw, I just thought there'd probably be something
in there.

See:
http://www.boost.org/doc/html/replace_all.html


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Isaac Rodriguez
Guest
PostPosted: Sat Apr 16, 2005 12:06 am    Post subject: Re: Replacing consecutive matching elements in a string Reply with quote


Quote:
I'm trying to use the STL to replace every time there are consecutive
tabs with ' ' in a string. I came up with something that works, but it
seems like there should be an easier way to do it. I'm looking for
another strategy, not really bug-fixes as this is semi-spaghetti code.
Also, I don't want to exploit the possibility of string iterators being
pointers. Thanx.

Well, I am not sure if this is simpler or not, but you can take a look at
it.

#include <iostream>
#include <string>
#include <algorithm>


int main ()
{
using std::string;
using std::cout;
using std::endl;

string s = "HellottWorldtthisttisttfun";
cout << s << endl;

string::iterator search = s.begin();
while ( search != s.end() ) {

search = std::find(search, s.end(), 't');
if (search != s.end()) {

string::iterator next = search + 1;
if (*next == *search && 't' == *search) {

s.replace(search, next + 1, 1, ' ');
}
else {

++search;
}
}
}

cout << s << endl;

return 0;
}

- Isaac.



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Carl Barron
Guest
PostPosted: Sat Apr 16, 2005 5:40 pm    Post subject: Re: Replacing consecutive matching elements in a string Reply with quote
Isaac Rodriguez <discussion.support (AT) autodesk (DOT) com> wrote:

Quote:
I'm trying to use the STL to replace every time there are consecutive
tabs with ' ' in a string. I came up with something that works, but it
seems like there should be an easier way to do it. I'm looking for
another strategy, not really bug-fixes as this is semi-spaghetti code.
Also, I don't want to exploit the possibility of string iterators being
pointers. Thanx.

Well, I am not sure if this is simpler or not, but you can take a look at
it.
...

as long as you are looking at std::strings, why not

void replace_all(std::string &str,std::string const &fnd,std::string
const & rep)
{
std::string::size_type pos=0;
std::string::size_type len=fnd.length();
std::string::size_type rep_len = rep.length();

while((pos = str.find(fnd,pos)) !=std::string::npos)
{
str.replace(pos,len,rep);
pos+=rep_len;
}
}

The code is for exposition only, not tested.



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Seungbeom Kim
Guest
PostPosted: Sat Apr 16, 2005 5:43 pm    Post subject: Re: STL: Replacing consecutive matching elements in a string Reply with quote
[email]lotusny78 (AT) yahoo (DOT) com[/email] wrote:
Quote:
Hi everyone,

I'm trying to use the STL to replace every time there are consecutive
tabs with ' ' in a string. I came up with something that works, but it
seems like there should be an easier way to do it. I'm looking for
another strategy, not really bug-fixes as this is semi-spaghetti code.
Also, I don't want to exploit the possibility of string iterators being
pointers. Thanx.
- Sean

#include <string>
#include <algorithm>

using std::string;

void replace_all(string& s, const string& a, const string& b)
{
for (string::size_type i = s.find(a);
i != string::npos;
i = s.find(a, i + b.size()))
s.replace(i, a.size(), b);
}

replace_all(str, "tt", " ");

--
Seungbeom Kim

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Paavo Helde
Guest
PostPosted: Sun Apr 17, 2005 2:25 pm    Post subject: Re: STL: Replacing consecutive matching elements in a string Reply with quote
[email]lotusny78 (AT) yahoo (DOT) com[/email] wrote in news:1113537204.841335.52700
@l41g2000cwc.googlegroups.com:

Quote:
Hi everyone,

I'm trying to use the STL to replace every time there are consecutive
tabs with ' ' in a string. I came up with something that works, but it

Something like this? This replaces any sequence of 2 or more tabs by a
single space (note: untested).

string::size_type k=0;
while((k=line.find("tt", k))!=line.npos) {
string::size_type l = line.find_first_not_of("t", k);
line[k++] = ' ';
line.erase(k, l-k);
}

Paavo

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Thierry Miceli
Guest
PostPosted: Sun Apr 17, 2005 3:38 pm    Post subject: Re: STL: Replacing consecutive matching elements in a string Reply with quote
You may use the std::unique function template that takes a binary
predicate as follows:

class AdjacentBlanks
{
public:
bool operator()(char el1, char el2)
{
return ( el1 == ' ' && el2 == ' ' );
}
};

.......

// Replace all tabs by space characters
std::replace(line.begin(), line.end(), 't', ' ');

// Replace sequences of spaces by a single space character
std::unique(line.begin(), line.end(), AdjacentBlanks());


Thierry Miceli
www.ideat-solutions.com

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John Potter
Guest
PostPosted: Sun Apr 17, 2005 6:04 pm    Post subject: Re: STL: Replacing consecutive matching elements in a string Reply with quote
On 15 Apr 2005 03:27:40 -0400, [email]lotusny78 (AT) yahoo (DOT) com[/email] wrote:

Quote:
I'm trying to use the STL to replace every time there are consecutive
tabs with ' ' in a string. I came up with something that works, but it
seems like there should be an easier way to do it.

I assume that using the STL and easier means hiding the logic in one
liners.

Quote:
Also, I don't want to exploit the possibility of string iterators being
pointers.

String iterators are random access iterators whether they are pointers
or not. You can do anything with a random access iterator that you can
do with a pointer.

Quote:
if('t' == c1 && 't' == c2)
return true;
else
return false;

Sorry, I can't resist. Use one line.

return 't' == c1 && 't' == c2;

Let's assume no embedded nul characters, then the following should do
the job.

char f1 (char c1, char c2) {
return c2 == '' && c1 == 't' ? ' ' : c1;
}
char f2 (char c1, char c2) {
return c2 == 't' && c1 == 't' ? '' : c2;
}
void doubleTabToSpace (std::string& s) {
std::transform(s.begin(), s.end() - 1, s.begin() + 1,
s.begin() + 1, f2);
std::transform(s.begin(), s.end() - 1, s.begin() + 1,
s.begin(), f1);
s.erase(std::remove(s.begin(), s.end(), ''), s.end());
}

John

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Carl Barron
Guest
PostPosted: Sun Apr 17, 2005 9:21 pm    Post subject: Re: STL: Replacing consecutive matching elements in a string Reply with quote
<lotusny78 (AT) yahoo (DOT) com> wrote:

Quote:
Hi everyone,

I'm trying to use the STL to replace every time there are consecutive
tabs with ' ' in a string. I came up with something that works, but it
seems like there should be an easier way to do it. I'm looking for
another strategy, not really bug-fixes as this is semi-spaghetti code.
Also, I don't want to exploit the possibility of string iterators being
pointers. Thanx.
- Sean
struct two_tabs

{
bool operator () (char x,char y) const {return x=='t' && y=='t';}
}

void remove_mutliple_tabs(std::string &line)
{
std::string::iterator it = std::unique(line.begin(),line.end(),
two_tabs());
line.erase(it,line.end());
}


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John Potter
Guest
PostPosted: Sun Apr 17, 2005 9:21 pm    Post subject: Re: STL: Replacing consecutive matching elements in a string Reply with quote
On 17 Apr 2005 11:38:57 -0400, [email]tmiceli (AT) sympatico (DOT) ca[/email] (Thierry Miceli)
wrote:

Quote:
You may use the std::unique function template that takes a binary
predicate as follows:

// Replace all tabs by space characters
std::replace(line.begin(), line.end(), 't', ' ');

// Replace sequences of spaces by a single space character
std::unique(line.begin(), line.end(), AdjacentBlanks());

Ignoring the fact that this also changes existing space sequences
and replaces four tabs with a single space, unique only changes the
contents of the string, not the size.

line.erase(std::unique(line.begin(), line.end(), AdjacentBlanks()),
line.end());

It is worth noting that this is linear while most other solutions are
quadratic.

John

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Allan W
Guest
PostPosted: Tue Apr 19, 2005 11:00 pm    Post subject: Re: STL: Replacing consecutive matching elements in a string Reply with quote
Quote:
lotusny78 (AT) yahoo (DOT) com wrote:
I'm trying to use the STL to replace every time there are
consecutive tabs with ' ' in a string.

simont wrote:
Quote:
Perhaps something like
boost::algorithm::replace_all( str, "tt", " " );

But if there are five tabs in a row, this would only replace four of
them -- and it would replace them with two spaces instead of just one.

Maybe this (assumes no more than 80 tabs in a row in original string):
// 80 tabs
const char tabs[]="tttttttttttttttttttt"
"tttttttttttttttttttt"
"tttttttttttttttttttt"
"tttttttttttttttttttt";
for (int i=0; i boost::algorithm::replace_all(str, tabs+i, " ");

Or maybe this (assumes no more than about 16000 tabs in a row):
const char tabs[]="tttttttttttt"; // 12 tabs
int i;
// Strings of 18 or more tabs have 16 tabs removed...
for (i=0; i<999; ++i)
boost::algorithm::replace_all(str, tabs, tabs+10);
for (i=0; i<=10; ++i)
boost::algorithm::replace_all(str, tabs+i, " ");


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kanze@gabi-soft.fr
Guest
PostPosted: Wed Apr 20, 2005 12:34 pm    Post subject: Re: STL: Replacing consecutive matching elements in a string Reply with quote
Allan W wrote:
Quote:
lotusny78 (AT) yahoo (DOT) com wrote:

I'm trying to use the STL to replace every time there are
consecutive tabs with ' ' in a string.
simont wrote:
Perhaps something like
boost::algorithm::replace_all( str, "tt", " " );

But if there are five tabs in a row, this would only replace
four of them -- and it would replace them with two spaces
instead of just one.

Maybe this (assumes no more than 80 tabs in a row in original
string):
// 80 tabs
const char tabs[]="tttttttttttttttttttt"
"tttttttttttttttttttt"
"tttttttttttttttttttt"
"tttttttttttttttttttt";
for (int i=0; i boost::algorithm::replace_all(str, tabs+i, " ");

Or maybe this (assumes no more than about 16000 tabs in a row):
const char tabs[]="tttttttttttt"; // 12 tabs
int i;
// Strings of 18 or more tabs have 16 tabs removed...
for (i=0; i<999; ++i)
boost::algorithm::replace_all(str, tabs, tabs+10);
for (i=0; i<=10; ++i)
boost::algorithm::replace_all(str, tabs+i, " ");

Wouldn't boost::regex and boost::replace be a better solution,
with a regex pattern of "\t+" and a replace pattern of " "?

--
James Kanze GABI Software
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34


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John Potter
Guest
PostPosted: Wed Apr 20, 2005 3:52 pm    Post subject: Re: STL: Replacing consecutive matching elements in a string Reply with quote
On 19 Apr 2005 19:00:31 -0400, "Allan W" <allan_w (AT) my-dejanews (DOT) com>
wrote:

Quote:
lotusny78 (AT) yahoo (DOT) com wrote:
I'm trying to use the STL to replace every time there are
consecutive tabs with ' ' in a string.

simont wrote:
Perhaps something like
boost::algorithm::replace_all( str, "tt", " " );

But if there are five tabs in a row, this would only replace four of
them -- and it would replace them with two spaces instead of just one.

Exactly what the original code did. Why are you changing the problem?

John

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E. Mark Ping
Guest
PostPosted: Thu Apr 21, 2005 2:36 am    Post subject: Re: STL: Replacing consecutive matching elements in a string Reply with quote
In article <1113984974.749659.76450 (AT) l41g2000cwc (DOT) googlegroups.com>,
<kanze (AT) gabi-soft (DOT) fr> wrote:
Quote:
Allan W wrote:
[email]lotusny78 (AT) yahoo (DOT) com[/email] wrote:

I'm trying to use the STL to replace every time there are
consecutive tabs with ' ' in a string.

Wouldn't boost::regex and boost::replace be a better solution,
with a regex pattern of "\t+" and a replace pattern of " "?

Or better yet, a regex pattern of "\t\t+".
--
Mark Ping
[email]emarkp (AT) soda (DOT) CSUA.Berkeley.EDU[/email]

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