help me find out why it is like this

hello, im stuck in a simple loop,i dont know why this doesnt give me the expected result! im really really confused!
please help find the problem.

Code:

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#include <cstdlib>
#include <iostream>

using namespace std;

int main(int argc, char *argv[])
{
         
          string str = "sum: 5";
         
          char * cstr;
          char currentcharacter;
          char strvalue[15];
         
          cstr = new char [str.size()+1];
          strcpy (cstr, str.c_str());
           
          char * ptr;
          int found = str.find(':');
          int value=0,cnt=0;
         
    while( cstr[found]!='\0')
    {
          currentcharacter = cstr[ found];
         
          if ( (isspace(currentcharacter) ))
          {
                  found++;
                  continue;
          }
         
          ptr[ found] = cstr[ found];
          found++; 
                                         
    }

                   
                                                 
          value = atoi(ptr);
          cout<<ptr<<endl;
          cout<<value+10;
         
         
    system("PAUSE");
    return EXIT_SUCCESS;
}

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the ptr gets filled with garbage characters . !(or may be it doesnt ever get filled)

What are you trying to do? For example, what is the expected result and the actual result?

well , im trying to go through the string (starting from ':' checking the whole string , if any spaces is encountered , ignore em , when you find any digits copy them in another string , after that , im converting that string to integer . and etc .
so far it just gives me rubbish! it seems the loop is not working !!

1. ptr isn't allocated.
2. You should write to ptr[0] first, then ptr[1] etc (you need another counter)
3. You don't append a \0
4. You don't delete any memory you allocate
5. What does cstr.find() return if nothing is found?

Mmm, perhaps too many clues....

Your belief that ptr[found] exists is misguided.

You never allocated any memory for your ptr variable.

Quote:

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Originally Posted by Masterx

well , im trying to go through the string (starting from ':' checking the whole string , if any spaces is encountered , ignore em , when you find any digits copy them in another string , after that , im converting that string to integer . and etc .

---

So, str is the source string. Instead of manually managing the memory of a dynamically allocated C style string, use another std::string object as the destination string. You just need to loop over the characters of the source string and append them to the destination string if they are numeric. When you are done, you can convert the string to integer.

Alternatively, you can do without the destination string by directly "appending" the character to be in the one's place of the integer.

A few other things to note:

• Indent your code more consistently.
• #include <string> since you use std::string
• If you really wanted to use those null terminating string operations, you should have #include <cstring>

Quote:

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Originally Posted by Salem

1. ptr isn't allocated.
2. You should write to ptr[0] first, then ptr[1] etc (you need another counter)
3. You don't append a \0
4. You don't delete any memory you allocate
5. What does cstr.find() return if nothing is found?

Mmm, perhaps too many clues....

---

tanx , you mean instead of

Code:

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ptr[ found] = cstr[ found];

---

i must write

Code:

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int counter = 0;
ptr[counter++] = cstr [found];

---

?

and about

Quote:

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"3. You don't append a \0

---

is it not appended automaticly at the end of cstr?( i meant null terminating character( that resembles the end of the string)by writing !='\0')
would you explain more about number 4 and 5 ?

Maybe, but lets see if you can figure it out first ;)

Quote:

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Originally Posted by laserlight

So, str is the source string. Instead of manually managing the memory of a dynamically allocated C style string, use another std::string object as the destination string. You just need to loop over the characters of the source string and append them to the destination string if they are numeric. When you are done, you can convert the string to integer.

Alternatively, you can do without the destination string by directly "appending" the character to be in the one's place of the integer.

A few other things to note:

• Indent your code more consistently.
• #include <string> since you use std::string
• If you really wanted to use those null terminating string operations, you should have #include <cstring>

---

tanx , but howto loop through the "string str" string ? would this (while str!='\0') work?
and by the way , sorry to ask, but im a noob in strings !! ,

Why not use another std::string to hold you numeric characters. This could simply your life a bit.

Code:

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std::string numericString;
for(int i = 0; i < 5; i++){
    numericString.push_back('1');
}//for

---

Quote:

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Originally Posted by Masterx

howto loop through the "string str" string ? would this (while str!='\0') work?

---

No, since it is an idiom for null terminated strings, which std::string is (generally) not. A simple index based for loop will suffice:

Code:

---

for (std::string::size_type i = 0, len = str.length(); i != len; ++i)
{
    // Access str[i] here.
}

---

You could also use string iterators with a generic algorithm like say, std::copy_if (or at the moment: std::remove_copy_if since std::copy_if would only be around in C++0x).

Quote:

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Originally Posted by Salem

Maybe, but lets see if you can figure it out first ;)

---

tanx, that eliminated most of the garbage !only two of them appears now ( i think thats definitely has sth to with loop counters(it seems its out of the range ! it prints out the 5 (which it should , and knowing that 5 is the last character of the string , and seeing teh output as 5@#, i think this means looped more than enough, is that right?)

Quote:

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Originally Posted by prog-bman

Why not use another std::string to hold you numeric characters. This could simply your life a bit.

Code:

---

std::string numericString;
for(int i = 0; i < 5; i++){
    numericString.push_back('1');
}//for

---

---

i dont know about push_back stuff! would you explain , what this snippet does!?

Quote:

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Originally Posted by Masterx

i dont know about push_back stuff! would you explain , what this snippet does!?

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prog-bman's suggestion is just a duplicate of mine. The push_back appends the character to the back of the string. You might want to refer to some documentation on std::string, e.g., the entries in cppreference.com

Link.

Actually, I didn't know myself string had this method. I have always used += for appending.

Code:

---

std::string numericString;
for(int i = 0; i < 5; i++){
    numericString += '1';
}

---

Quote:

---

Originally Posted by laserlight

No, since it is an idiom for null terminated strings, which std::string is (generally) not. A simple index based for loop will suffice:

Code:

---

for (std::string::size_type i = 0, len = str.length(); i != len; ++i)
{
    // Access str[i] here.
}

---

You could also use string iterators with a generic algorithm like say, std::copy_if (or at the moment: std::remove_copy_if since std::copy_if would only be around in C++0x).

---

whats this ? and why is it there ? if we use using namespace std; do we still need to include "std::string::size_type" ?

Quote:

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Originally Posted by Masterx

whats this ? and why is it there ?

---

What do you mean? I merely provided an example of how to use an index based for loop to iterate over the characters of a string. You would need to combine this with std::string's push_back(), or whatever method you wish to use to append to the destination string.

Quote:

---

Originally Posted by Masterx

if we use using namespace str; do we still need to include "std::string::size_type" ?

---

You would not need to fully qualify std::string::size_type, so you could write it as string::size_type. std::string::size_type is the index type of std::string.

Quote:

---

Originally Posted by laserlight

What do you mean? I merely provided an example of how to use an index based for loop to iterate over the characters of a string. You would need to combine this with std::string's push_back(), or whatever method you wish to use to append to the destination string.


You would not need to fully qualify std::string::size_type, so you could write it as string::size_type. std::string::size_type is the index type of std::string.

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tanx alot. im going to test these . i'll let you know , if i was successful.

soorry to bother , thanks alot Dears. it went all fine , but i got some problem , i cant use "atoi() with string ! what should i do now ?atol() ? does it make it?

Code:

---

for (string::size_type i = found, len = str.length(); i != len; ++i)
    {
          currentcharacter = str[i];
         
          if ( (isspace(currentcharacter) ))
          {
                 
                  continue;
          }
         
          str1+= str[i];

---

Quote:

---

Originally Posted by Masterx

i cant use "atoi() with string ! what should i do now ?atol() ? does it make it?

---

You actually "solved" this problem in your original code by using the c_str() member function of std::string.

Quote:

---

Originally Posted by laserlight

You actually "solved" this problem in your original code by using the c_str() member function of std::string.

---

yeah , tanx for saying that . but my intention of asking such a question was that , i just want to know if there is any equivalent for string in C++! ? is there ? !

by the way , how could you guys understand that ptr was not allocated ! ? by experience or just its the knowledge of C++ that i can find in books/.?

Stringstreams.

Code:

---

string s("12345");
int n;
stringstream ss(s);
ss >> n;

---

Quote:

---

Originally Posted by Masterx

by the way , how could you guys understand that ptr was not allocated ! ? by experience or just its the knowledge of C++ that i can find in books/.?

---

Generally it's called "reading the code". You start at the top and you go to the bottom (going around and around in loops, naturally). You used ptr, but you never created any memory for it to point to.

Quote:

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Originally Posted by anon

Stringstreams.

Code:

---

string s("12345");
int n;
stringstream ss(s);
ss >> n;

---

---

many tanx. now i got it .the use of stringstream that Elysia and laiserlight used to tell me multiple times and i couldnt understand how it works! lol)

Quote:

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Originally Posted by tabstop

Generally it's called "reading the code". You start at the top and you go to the bottom (going around and around in loops, naturally). You used ptr, but you never created any memory for it to point to.

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many tanx for the info dear tabstop.