Replacing std::strings

Question

My string is std::string str ("DDWD");

I want to change the corresponding to the following

D = [0-9] W = [a-z]

soo...("[0-9][0-9][A-Z][0-9]")

The replace method does not seem to accomade this, so i tried something like

string tmp = "DDDWD";   
int len = 0;   
len = tmp.length();   
for( int i = 0; i < len; i++ )
{
    if ( tmp[i] == 'D')
    {  
        tmp.replace(i,1,"[0-9]");  
        i+=2;  
    }
}

However trying to change both letters D and W there was a problem and it wasent changing them all correctly?

Does anyone know a way how to change each letter at the same time to the corresponding string above?

Thankful for any help

What is the "problem"? What is the output you actually got? What did you observe when you stepped through this in the debugger? — Oliver Charlesworth, Jan 07 '12 at 16:31
See this [link](http://stackoverflow.com/questions/1494399/how-do-i-search-find-and-replace-in-a-standard-string) — Siva Karuppiah, Jan 07 '12 at 16:40

score 3 · Answer 1 · answered Jan 07 '12 at 16:32

3

Looks to me like you're just ending your loop early.

len = tmp.length();

for( int i = 0; i < len; i++ )

{

...so you save the length to iterate, and even if the string gets longer, you'll stop at the old length.

answered Jan 07 '12 at 16:32

sje397

41,293
8
87
103

Benjamin Lindley · Accepted Answer · 2012-01-07T16:43:15.160

2

I think this would be cleaner if you used a separate string:

string tmp = "DDDWD";
string tmp2;

for (int i=0; i<tmp.size(); ++i)
{
    if (tmp[i] == 'D')
        tmp2 += "[0-9]";
    else if (tmp[i] == 'W')
        tmp2 += "[a-z]";
    else
        tmp2 += tmp[i];
}

tmp.swap(tmp2);

// or in C++11
// tmp = std::move(tmp2);

edited Jan 07 '12 at 16:43

answered Jan 07 '12 at 16:35

Benjamin Lindley

101,917
9
204
274

score 1 · Answer 3 · answered Jan 07 '12 at 16:36

The replace method works with positions, not substrings. So replacing would be a two-step process: find first, then replace with the results of the find, until find no longer finds anything.

But the way you do it also works, if you run the loop backwards (start at the end and work your way down).

score 0 · Answer 4 · answered Jan 07 '12 at 23:41

If you can afford it, use Boost's String Algo library. It has lots of useful algorithms on strings. Your problem would then read:

  // #include <boost/algorithm/string/replace.hpp>
  std::string tmp = "DDDWD"; 
  boost::replace_all( tmp, "D", "[0-9]" );
  boost::replace_all( tmp, "W", "[a-z]" );

score -1 · Answer 5 · answered Jan 07 '12 at 16:57

-1

int main()
{
  std::string tmp = "DDDWD";
  char *tmp2=new char(5*(strlen(tmp.c_str()) +1)); 
  cout << "tmp is " << tmp;


  for (int i=0; i<tmp.size(); ++i)
  {
    if (tmp[i] == 'D' && i==0)
    tmp2 = strcpy(tmp2,"[0-9]");
    else if(tmp[i] == 'D' && i!=0) 
    tmp2 = strcat(tmp2,"[0-9]");   
    else if (tmp[i] == 'W' && i==0)
    tmp2 = strcpy(tmp2,"[a-z]");
    else if (tmp[i] == 'W' && i!=0)
    tmp2 = strcat(tmp2,"[a-z]");
  }

  cout << "tmp2 is :" << tmp2;

  getchar();   
}

answered Jan 07 '12 at 16:57

Invictus

4,028
10
50
80

1

If you null-terminate tmp2 from the start, you can just use strcat everytime. Then you don't need the extra logic of checking if `i==0` or `i!=0` – Benjamin Lindley Jan 07 '12 at 17:24
@Andrzej I tried implementing the boost thing you mentioned , but i get an error saying it is not able to include replace.hpp file as you mentioned . Is it not available in standard C++ – Invictus Jan 08 '12 at 10:31

Replacing std::strings

5 Answers5