Question

Converting a string to char array

Asked by: girionis

Hello I have the following code:

#include <iostream.h>
#include <fstream.h>
#include <string>
#include <iomanip>

int length(const char* str)
{
      int length;
      for (int i=0;str[i]!='\0'; i++)
      {
            length=i;
      }

      return length;
}

void break_lines(string buf)
{
      const char* str;
      strcpy(str, buf); <<<-------------------------- HERE

      int l = length(str);
      char buffer[l+1];
      for (int i=0, j=0;i<=l; i++)
      {
            if (str[i] != ' ')
            {
                  buffer[j] = str[i];
            }
            else
            {
                  cout << buffer << endl;
            }
      }
      
}

int readFile()
{
      ifstream inFile("rules.txt");

      string line;

      while (!inFile.eof())
      {
          getline(inFile, line);
            break_lines(line);
          cout<<line<<endl;
      }

      inFile.close();
      return 0;
}

int main()
{
      readFile();

      return 0;
}


I would like to convert the "buf" variable to "str" character array but I get the following error:

c:\applications\quincy99\assignment\start.cpp: In function `void break_lines(basic_string<char,string_char_traits<char>,__default_alloc_template<false,0> >)':
c:\applications\quincy99\assignment\start.cpp:20: passing `const char *' as argument 1 of `strcpy(char *, const char *)' discards qualifiers
c:\applications\quincy99\assignment\start.cpp:20: cannot convert `buf' from type `string' to type `const char *'

Any help of how I can do it is appreciated.

I am using the g++ compiler.

Regards

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Asked On
2004-07-01 at 11:36:48ID21045142
Tags

string

,

char

,

array

Topic

C++ Programming Language

Participating Experts
3
Points
200
Comments
7

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Answers

 

by: jaime_olivaresPosted on 2004-07-01 at 11:41:21ID: 11450295

Use:
   strcpy(str, buf.c_str());

 

by: jaime_olivaresPosted on 2004-07-01 at 11:42:46ID: 11450309

But wait!!! str is not initialized!!!

you can use:
char *str = new char[100]; // choose your size

or directly:
char str[100];

 

by: jaime_olivaresPosted on 2004-07-01 at 11:45:15ID: 11450333

Also you can use direct pointer reference:

const char *str = buf.c_str();

instead of strcpy();

 

by: jkrPosted on 2004-07-01 at 11:48:55ID: 11450373

Use

void break_lines(string buf)
{
    char* str = strdup ( buf.c_str());

    // ....

    free ( str);
}

You are performing manipulations on the string, so you should copy the contents before doing so in order to avoid problems.

 

by: jaime_olivaresPosted on 2004-07-01 at 12:03:01ID: 11450505

> You are performing manipulations on the string, so you should copy the contents before doing so in order to
> avoid problems.
I don't see where STL string is altered. If not, it is not necessary to duplicate.

 

by: girionisPosted on 2004-07-01 at 12:38:52ID: 11450856

Thank you, it worked :)

Also, thank you jkr for your suggestion too :)

 

by: AxterPosted on 2004-07-01 at 12:57:22ID: 11451014

FYI:
Both <iostream.h> and <fstream.h> are *not* part of the C++ standard, and therefor not portable.

You should use extensionless version instead.
#include <iostream>
#include <fstream>

20120131-EE-VQP-002

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