Re: a simple phonebook program,get into a loop.
On Aug 20, 8:29 am, jerry <machel2...@yahoo.cn> wrote:
i have written a simple phonebook program,i'll show you some of the
codes,the program's head file is member.h . i suppose the head file
works well.so i don't post it. here's the clips of main function
which i think has problem
// this a simple program about phonebook,it can add items,del
items,find items and
#include "member.h"
#include <fstream>
#include <vector>
#include <iostream>
using namespace std;
int DoMenu(); //display menu
void DoAdd(); //add items
void Write(); // write vector into file
string FileName;
vector <Member> phoneBook;
Global variables. Yuck. Put these in main() and pass them into the
function (unless your teacher told you to do it this way for now, or
something).
int main()
{
enum CHOICE{Exit,Add};
You define this enum here but then hard code these same values into
the prompt in DoMenu() below. That's fine for a program of this size,
but you should develop good habits now for when you work on bigger
projects. In particular, make this type global so that both functions
that use it (or should use it since the one is implicitly duplicating
it) can see it.
bool exit = false;
cout << "Enter the Name of your PhoneBook: " << endl;
cin >> FileName;
while(!exit) =
//while exit is false,let user
input choice
{
int choice = DoMenu();
switch(choice) =
// do the action user select
{
case Exit:
exit = true;
break;
case Add:
DoAdd();
break;
default:
cerr << "Input error! try=
again!" << endl;
break;
}
}
return 0;
}
int DoMenu()
{
int choice;
cout << "Input your choice" << endl;
cout << "(0) Exit (1) Add item (2)Del item (3)Find item (=
4)Read
phonebook: " << endl;
cin >> choice;
return choice;
}
void DoAdd() //it will add items custom input=
,the add it
to vector phoneBook
{ // then call=
write function to write vector
phoneBook into file
string OneName;
string OneAdd;
string OneNum;
cout << "Input name: ";
getline(cin,OneName);
cout << "Input address: ";
getline(cin,OneAdd);
cout << "Input phonenumber: ";
getline(cin,OneNum);
You should be making sure your getline calls worked. See the FAQ
below.
Member newRecord(OneName,OneAdd,OneNum);
phoneBook.push_back(newRecord);
Write();
}
void Write()
{
ofstream fout;
fout.open (FileName.c_str(),ios::out | ios::trunc);
First, you can use the constructor to open the file like this:
ofstream fout( FileName.c_str(), ios::out | ios::trunc );
Second, do you really want to truncate (i.e., erase) the file each
time you call Write()? Try ios::app or ios::ate instead. Ultimately, I
suppose you'll be reading the whole thing in at startup and writing it
out on exit, and then you would want to truncate it. In that case,
however, you don't need to specify any flags since that is the default
behavior. Hence your code would read:
ofstream fout( FileName.c_str() );
Much cleaner and easier to read.
if (!fout.is_open ())
cerr << "Can't open file" << FileName << endl;
This condition doesn't check for failed state. Use something like this
instead:
if( !fout ) { /*...*/ }
Note that you should also return or put the writing code in an else
block or something. As it stands, on failure to open the file, your
function still tries to write.
fout.write((char *)&phoneBook,sizeof(phoneBook)); /=
/why
can't dump &
First of all, use the formatted output operator <<, like you do with
cout. The iostream read and write functions are for unformatted (most
often, binary) I/O, not vanilla text I/O like you're doing. Second,
you're trying to write out a vector, not the *contents* of the vector.
A vector is a container class that maintains a few things to keep
track of the actual contents, and you don't really care about saving
those housekeeping details. Try something like:
fout << phoneBook[0].name << '\n'
<< phoneBook[0].address << '\n'
<< phoneBook[0].phone << '\n';
(I guess on the member names since you didn't include the header.) You
can put this in a loop in various ways (note that I'm checking the
file's state in the for-loop's condition; this is best, but it could
be omitted for a tiny program like this):
for( size_t n=0; fout && n < phoneBook.size(); ++n )
fout << phoneBook[ n ].name << '\n' /*...*/;
Or
typedef vector<Member>::iterator iter;
for( iter it = phoneBook.begin(); fout && it != phoneBook.end(); +
+it )
fout << it->name << '\n' /*...*/;
There are other snazzier ways to do it like defining a << operator for
your Member class, which would allow you to write:
fout << phoneBook[0] << '\n';
or to use std::copy and std::ostream_iterator, but that is for another
day.
fout.close();
FWIW, the fstream will close automatically when you exit this
function, so you don't need to explicitly close it here. You might
want to explicitly close a file sometimes, but here it's optional and
just more code to write.
}
when i select item Add,after i input name,address,phone number. this
program will get into a loop.as below:
Input error! try again!
Input your choice
(0) Exit (1) Add item (2)Del item (3)Find item (4)Read phonebook:
those three line are filled with cmd windows.
See these FAQs:
http://www.parashift.com/c++-faq-lite/input-output.html#faq-15.2
http://www.parashift.com/c++-faq-lite/input-output.html#faq-15.3
http://www.parashift.com/c++-faq-lite/input-output.html#faq-15.6
ps. why can't i write fout.write((char
*)&phoneBook,sizeof(phoneBook)); as fout.write((char
*)phoneBook,sizeof(phoneBook));
See above.
Cheers! --M