How do i convert a string to a character array?

How do i convert a string to a character array?

We are using a command line prompt like this:
int main(int argc, char **argv)

We put the argv into a string variable like this:
ipstring = argv[1];
so we could parse the string using string member functions.

We tried an atoi on ipstring but atoi would not work we got:

error C2664: 'atoi' : cannot convert parameter 1 from 'class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >' to 'const char *'
No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called

Any help would be greatly appreciated.
Susan

Use the c_str() member function.

tried this
cout << "/n this is chunk1 = " << ipchunk1.c_str() << endl;

Execution/run time error:
the instruction at 0x00422820 referenced memory at
0x00000000. The memory could not be "read."

i like string but i don't know how to convert it to any other data type.
how can i convert from string to char and how can i convert to integer?

thanks,
susan

PS I am trying to help my son who is trying to write code just for his own interest. he hopes to take computer classes next fall when he will be a freshman in college.

http://www.cppreference.com/cppstring.html

Here is a good reference for the string class.
Also in that line of code you posted, the /n should be \n

Code:

---

#include <string>
#include <iostream>
#include <stdlib.h>
using namespace std;

int main() {
  string sStr = "1234";
  int iNum = atoi(sStr.c_str());
  cout << iNum << endl;
  return 0;
}

---

This works fine under Visual C++. Substitute "1234" by an argument you need to convert.

I think your problem is connected with the fact that you can't do '=' with 0-terminated strings outside of declarations.

There are at least 4 different common string "systems" in C++ which I identified in my notes by which include file you need:

// cstring standard header -- not sure what this is
#include <string.h>

// Microsoft.
string.h - declarations for string manipulation functions

<string> classname is basic_string
//I think this is a more elaborate and usefule string class

<cstring>
//I think this is the char* 0-terminated strings you're looking for

FACTS about cstrings
1: array size declared must be const;
const int max=50; char ar[max];

2: arrays don't allow '=' outside of decl,
char ar[]="hello"; ok but later ar="goodbye" not ok; but cin >>ar OK

3: in strcpy(targ,srce) targ must be ar[] with known size
in strtok(inString,del) inString must be ar[] with known size

4: ptrs allow = assignments after declare: via "literal" or otherwise
therefore, function outputs must always be ptrs

5: after decl: ptr '=' X makes alias; actions on ptr change X
but a later ptr'='Y make Y-alias, cancels X-alias

6. no '+' for concat, i.e. NOT s="banana"+"banana"

FUNCTIONS: STRCAT, STRNCAT, STRCMP, STRNCMP, STRCPY, STRNCPY, STRLEN, STRTOK,

Good luck, Al

<cstring> includes string.h

Back when there was just C, the string.h header file was made up with all those nice char *(aka strings) manilplation functions.
Now there is C++ and there is the STL string class.
The name cstring comes from the fact they were string's for C.

#include <cstring> or #include <string.h>
for the functions STRCAT, STRNCAT, STRCMP, STRNCMP, STRCPY, STRNCPY, STRLEN, STRTOK,
#include <string> to use the string class

thank you all very much. I miss PL1. that is how old of a programmer i am!
C++ - so many ways to do something that should be simple.
well, my son's program is running thanks to you all.
Happy New Year!
Susan

Now that the problems solved and I can no longer help, I just want to point out, Borland's manuals give excellent instructions on command-line parameters if anyone elkse has questions relating to the subject.