get(char*, num, delim) question

[Francis Bell]

Hello,

I've got a program that is reading in a data file of 25 lines. Here is
an example of the first two lines:

sp/spinnerbait/AAA Lures/Mad Phil/silver/bass/1/1
f/floating minnow/AAA Lures/Skinny Minney/green/bass/0/0/0

In my program, I need to read in each line, BUT, I need to build a
different object based upon the characters in the first field. So, I
need to GET the first characters. And here's where I'm doing something
incorrectly. This is what I've got so far:

char readInFirstChar s(ifstream &fin) {
char *first;
fin.get(first, 3, '/');
cout << first; // debugging line to see what is output
}
return first;
}

The above code give me a compile error stating:
" invalid conversion from `char*' to `char'"

I tried the get function with the single character parameter like such:
char first;
fin.get(first);
cout << first << endl;
return first;

and it works fine. So I must be doing something wrong with the pointer.

The other tangent problem I'm having with this how to properly cycle
through the input file so it only reads in the first field and then
moves on to the next line. I tried
while (fin.good()) {
char first;
fin.get(first);
cout << first << endl;
}
return first;

Which looped, but it output the entire file. I only need the first
field. If the first field were only one character, then the only
problem I would be dealing with is the loop problem, but since it's
either 1 or 2 characters (with the end delimeter being '/'), I'm also
dealing with the get() problem.

Thanks for any advice.

Frank

[John Harrison]

"Francis Bell" <ph**********@c harter.net> wrote in message
news:10******** *****@corp.supe rnews.com...

Hello,

I've got a program that is reading in a data file of 25 lines. Here is
an example of the first two lines:

sp/spinnerbait/AAA Lures/Mad Phil/silver/bass/1/1
f/floating minnow/AAA Lures/Skinny Minney/green/bass/0/0/0

In my program, I need to read in each line, BUT, I need to build a
different object based upon the characters in the first field. So, I
need to GET the first characters. And here's where I'm doing something
incorrectly. This is what I've got so far:

char readInFirstChar s(ifstream &fin) {
char *first;
fin.get(first, 3, '/');
cout << first; // debugging line to see what is output
}
return first;
}

The above code give me a compile error stating:
" invalid conversion from `char*' to `char'"

I tried the get function with the single character parameter like such:
char first;
fin.get(first);
cout << first << endl;
return first;

and it works fine. So I must be doing something wrong with the pointer.

Yes, two different things actually. And of course you should be using a
pointer at all. Try this

char first[3];
fin.getline(fir st, 3, '/');

Important lesson is to understand the difference between

char *first;

and

char first[3];

The first declares a pointer to char, it does not create any characters at
all. Just declaring a pointer does not make it point at anything. So in your
code you do not have any characters to read the first field into. Even if
you had got it to compile it would have crashed when you tried to do the
read.

The second declares an array of three characters, these are the three
characters you are going to read your field into. No need for compilcated
pointers, just use an array.

Your second mistake was to use get instead of getline.

john

[Francis Bell]

John Harrison wrote:

"Francis Bell" <ph**********@c harter.net> wrote in message
news:10******** *****@corp.supe rnews.com...

Hello,

I've got a program that is reading in a data file of 25 lines. Here is
an example of the first two lines:

sp/spinnerbait/AAA Lures/Mad Phil/silver/bass/1/1
f/floating minnow/AAA Lures/Skinny Minney/green/bass/0/0/0

In my program, I need to read in each line, BUT, I need to build a
different object based upon the characters in the first field. So, I
need to GET the first characters. And here's where I'm doing something
incorrectly . This is what I've got so far:

char readInFirstChar s(ifstream &fin) {
char *first;
fin.get(first, 3, '/');
cout << first; // debugging line to see what is output
}
return first;
}

The above code give me a compile error stating:
" invalid conversion from `char*' to `char'"

I tried the get function with the single character parameter like such:
char first;
fin.get(first);
cout << first << endl;
return first;

and it works fine. So I must be doing something wrong with the pointer.

Yes, two different things actually. And of course you should be using a
pointer at all. Try this

char first[3];
fin.getline(fir st, 3, '/');

Important lesson is to understand the difference between

char *first;

and

char first[3];

The first declares a pointer to char, it does not create any characters at
all. Just declaring a pointer does not make it point at anything. So in your
code you do not have any characters to read the first field into. Even if
you had got it to compile it would have crashed when you tried to do the
read.

The second declares an array of three characters, these are the three
characters you are going to read your field into. No need for compilcated
pointers, just use an array.

Your second mistake was to use get instead of getline.

john

Hi John,
First, thanks for the quick reply! Unfortunately, I have been
instructed to use the get() function vice the getline() function. From
what I understand about the get() function with the three parameters, it
reads characters into a buffer until num - 1 characters have been read,
or in my case, until the '/' delim character is encountered. This way,
if it reads a line where the first field is only one character, it reads
that character and then encounters the '/' delimeter and stops. But
it's the first parameter that I'm not doing correctly. ... However,
what you said about me having just declared a pointer and not pointing
to anything made me think of something. And I just tried something else
and it worked for both of my problems! This is what I did:

while (fin.good())
{
fin.get(first, 4, '/');
cout << first << endl;
fin.ignore(80, '\n');
}
delete [] first;

This displays 'sp' to the screen for that first line of text in the data
file and 'f' for the second line, and the first field for all of the
other lines until EOF.

So now I'm on to the next problem in my program. But I'll work on that
for a few hours before posting back if I need to. Thanks again John for
looking at this. Although I couldn't use the getline as you suggested,
your suggestion pointed me to my problem. Thanks!

Frank

[John Harrison]

"Francis Bell" <ph**********@c harter.net> wrote in message
news:10******** *****@corp.supe rnews.com...

John Harrison wrote:

"Francis Bell" <ph**********@c harter.net> wrote in message
news:10******** *****@corp.supe rnews.com...

Hello,

I've got a program that is reading in a data file of 25 lines. Here is
an example of the first two lines:

sp/spinnerbait/AAA Lures/Mad Phil/silver/bass/1/1
f/floating minnow/AAA Lures/Skinny Minney/green/bass/0/0/0

In my program, I need to read in each line, BUT, I need to build a
different object based upon the characters in the first field. So, I
need to GET the first characters. And here's where I'm doing something
incorrectly . This is what I've got so far:

char readInFirstChar s(ifstream &fin) {
char *first;
fin.get(first, 3, '/');
cout << first; // debugging line to see what is output
}
return first;
}

The above code give me a compile error stating:
" invalid conversion from `char*' to `char'"

I tried the get function with the single character parameter like such:
char first;
fin.get(first);
cout << first << endl;
return first;

and it works fine. So I must be doing something wrong with the pointer.

Yes, two different things actually. And of course you should be using a
pointer at all. Try this

char first[3];
fin.getline(fir st, 3, '/');

Important lesson is to understand the difference between

char *first;

and

char first[3];

The first declares a pointer to char, it does not create any characters at all. Just declaring a pointer does not make it point at anything. So in your code you do not have any characters to read the first field into. Even if you had got it to compile it would have crashed when you tried to do the
read.

The second declares an array of three characters, these are the three
characters you are going to read your field into. No need for compilcated pointers, just use an array.

Your second mistake was to use get instead of getline.

john

Hi John,
First, thanks for the quick reply! Unfortunately, I have been
instructed to use the get() function vice the getline() function.

Any particular reason?
From
what I understand about the get() function with the three parameters, it
reads characters into a buffer until num - 1 characters have been read,
or in my case, until the '/' delim character is encountered.
Yes, I'd forgotten about that, which is why I recommended getline,.but get
works too. The difference between get and getline, is that getline reads the
delimiter whereas get doesn't.
This way,
if it reads a line where the first field is only one character, it reads
that character and then encounters the '/' delimeter and stops. But
it's the first parameter that I'm not doing correctly. ... However,
what you said about me having just declared a pointer and not pointing
to anything made me think of something. And I just tried something else
and it worked for both of my problems! This is what I did:

I guess you missed out

char* first = new char[4];

or something similar.
while (fin.good())
{
fin.get(first, 4, '/');
cout << first << endl;
fin.ignore(80, '\n');
}
delete [] first;

Its still preferable to use an array instead of a pointer. Its more
efficient, safer and simpler, what's not to like?

Also you loop is wrong. The file might still be good even when you are at
the end of the file so you end up going round the loop one too many times.
Your loop should look like this

while (fin.get(first, 4, '/'))
{
cout << first << endl;
fin.ignore(80, '\n');
}

john

[Phrank]

On Sat, 22 May 2004 22:54:45 +0100, "John Harrison"
<jo************ *@hotmail.com> wrote:

"Francis Bell" <ph**********@c harter.net> wrote in message
news:10******* ******@corp.sup ernews.com...

John Harrison wrote:

> "Francis Bell" <ph**********@c harter.net> wrote in message
> news:10******** *****@corp.supe rnews.com...
>
>>Hello,
>>
>>I've got a program that is reading in a data file of 25 lines. Here is
>>an example of the first two lines:
>>
>>sp/spinnerbait/AAA Lures/Mad Phil/silver/bass/1/1
>>f/floating minnow/AAA Lures/Skinny Minney/green/bass/0/0/0
>>
>>In my program, I need to read in each line, BUT, I need to build a
>>different object based upon the characters in the first field. So, I
>>need to GET the first characters. And here's where I'm doing something
>>incorrectly . This is what I've got so far:
>>
>>char readInFirstChar s(ifstream &fin) {
>>char *first;
>> fin.get(first, 3, '/');
>> cout << first; // debugging line to see what is output
>>}
>>return first;
>>}
>>
>>The above code give me a compile error stating:
>>" invalid conversion from `char*' to `char'"
>>
>>I tried the get function with the single character parameter like such:
>> char first;
>> fin.get(first);
>> cout << first << endl;
>> return first;
>>
>>and it works fine. So I must be doing something wrong with the pointer.
>
>
> Yes, two different things actually. And of course you should be using a
> pointer at all. Try this
>
> char first[3];
> fin.getline(fir st, 3, '/');
>
> Important lesson is to understand the difference between
>
> char *first;
>
> and
>
> char first[3];
>
> The first declares a pointer to char, it does not create any charactersat > all. Just declaring a pointer does not make it point at anything. So inyour > code you do not have any characters to read the first field into. Evenif > you had got it to compile it would have crashed when you tried to do the
> read.
>
> The second declares an array of three characters, these are the three
> characters you are going to read your field into. No need forcompilcated > pointers, just use an array.
>
> Your second mistake was to use get instead of getline.
>
> john
>
>

Hi John,
First, thanks for the quick reply! Unfortunately, I have been
instructed to use the get() function vice the getline() function.

Any particular reason?

From
what I understand about the get() function with the three parameters, it
reads characters into a buffer until num - 1 characters have been read,
or in my case, until the '/' delim character is encountered.

Yes, I'd forgotten about that, which is why I recommended getline,.but get
works too. The difference between get and getline, is that getline reads the
delimiter whereas get doesn't.

This way,
if it reads a line where the first field is only one character, it reads
that character and then encounters the '/' delimeter and stops. But
it's the first parameter that I'm not doing correctly. ... However,
what you said about me having just declared a pointer and not pointing
to anything made me think of something. And I just tried something else
and it worked for both of my problems! This is what I did:

I guess you missed out

char* first = new char[4];

or something similar.

while (fin.good())
{
fin.get(first, 4, '/');
cout << first << endl;
fin.ignore(80, '\n');
}
delete [] first;

Its still preferable to use an array instead of a pointer. Its more
efficient, safer and simpler, what's not to like?

Also you loop is wrong. The file might still be good even when you are at
the end of the file so you end up going round the loop one too many times.
Your loop should look like this

while (fin.get(first, 4, '/'))
{
cout << first << endl;
fin.ignore(80, '\n');
}

john

Yeah, sorry, I forgot to copy and paste the pointer declaration. What
you put is accurate. This project is for a class, and my lab
instructor said we needed to use get() because we need the practice
with it. Although an array may be safer and simpler, this form of
get() that I needed to use doesn't allow for an array in the
parameters, otherwise I would have used it (primarily because I'm just
now getting used to pointers and I know that I know just enough about
them to be dangerous: :) ) I'll use the loop enhancement. Thanks
again John!!

Frank

[Siemel Naran]

Francis Bell <ph**********@c harter.net> wrote in message

sp/spinnerbait/AAA Lures/Mad Phil/silver/bass/1/1
f/floating minnow/AAA Lures/Skinny Minney/green/bass/0/0/0

char first[3];
fin.getline(fir st, 3, '/');

while (fin.good())
{
fin.get(first, 4, '/');
cout << first << endl;
fin.ignore(80, '\n');
}
delete [] first;

How did you declare first? If as char first[4] then the call to
delete is unnecessary, and will, in some systems, cause a program
crash.

[Francis Bell]

Siemel Naran wrote:

Francis Bell <ph**********@c harter.net> wrote in message

sp/spinnerbait/AAA Lures/Mad Phil/silver/bass/1/1
f/floating minnow/AAA Lures/Skinny Minney/green/bass/0/0/0
char first[3];
fin.getline( first, 3, '/');

while (fin.good())
{
fin.get(first, 4, '/');
cout << first << endl;
fin.ignore(80, '\n');
}
delete [] first;

How did you declare first? If as char first[4] then the call to
delete is unnecessary, and will, in some systems, cause a program
crash.

Hi all,

I declared first like this:

void readInFirstChar s(ifstream &fin)
{
char* first;
first = new char[2];
while (fin.good())
{
fin.get(first, 4, '/');
cout << first << endl;
fin.ignore(80, '\n');
}
cout << "Here first" << endl;
if (first == "sp") {
cout << "Here second" << endl;
Spinnerbait temp;
readInASpinnerb ait(fin);
temp.outputSpin nerbait(cout);
}
delete [] first;

I included my whole function because I spoke too soon earlier when I
said everything worked. My function is not getting inside the 'if'
clause. I know this because "Here first" is printing out to the screen,
but "Here second" is not. I'm pretty sure it's because of my condition
(first == "sp"). I know first is a pointer to my character array that
gets my first field from the data file, so comparing it with "sp" is
probably, no IS incorrect. But I tried dereferencing first and
comparing, and I got a compile error stating, "ISO C++ forbids
comparison between pointer and integer". So, that said, how do I go
about comparing these?

[John Harrison]

>

Yeah, sorry, I forgot to copy and paste the pointer declaration. What
you put is accurate. This project is for a class, and my lab
instructor said we needed to use get() because we need the practice
with it. Although an array may be safer and simpler, this form of
get() that I needed to use doesn't allow for an array in the
parameters,

That is not true, an array and a pointer are equivalent in this situation
(as they are in most situations).

john

[John Harrison]

> Hi all,

I declared first like this:

void readInFirstChar s(ifstream &fin)
{
char* first;
first = new char[2];
first = new char[4];

but as I said earlier you should be using an array

char first[4];

In either case though you need four characters, if you are going to say
fin.get(first, 4, '/');
while (fin.good())
{
fin.get(first, 4, '/');
cout << first << endl;
fin.ignore(80, '\n');
}
cout << "Here first" << endl;
if (first == "sp") {
This is wrong, you do not compare strings with ==

if (strcmp(first, "sp") == 0)
cout << "Here second" << endl;
Spinnerbait temp;
readInASpinnerb ait(fin);
temp.outputSpin nerbait(cout);
}
delete [] first;
Get rid of this if you switch to an array.

I included my whole function because I spoke too soon earlier when I
said everything worked. My function is not getting inside the 'if'
clause. I know this because "Here first" is printing out to the screen,
but "Here second" is not. I'm pretty sure it's because of my condition
(first == "sp"). I know first is a pointer to my character array that
gets my first field from the data file, so comparing it with "sp" is
probably, no IS incorrect.
No, first == "sp" is a pointer comparison, it compares where first is
pointing to with where "sp" is. You need strcmp to copare the strings
themeselves.
But I tried dereferencing first and
comparing, and I got a compile error stating, "ISO C++ forbids
comparison between pointer and integer". So, that said, how do I go
about comparing these?

Seems like you are learning an old fashioned style of C++ programming.
Modern C++ has a string class which is easier to use than a char array (or
char pointer).

john

[Siemel Naran]

Francis Bell <ph**********@c harter.net> wrote in message

sp/spinnerbait/AAA Lures/Mad Phil/silver/bass/1/1
f/floating minnow/AAA Lures/Skinny Minney/green/bass/0/0/0 void readInFirstChar s(ifstream &fin)
{
char* first;
first = new char[2];
It's fine to just say
char first[2];
and remove the delete statement below.
while (fin.good())
{
fin.get(first, 4, '/');
Why is first of 2 chars but you read 4 chars into it?
cout << first << endl;
fin.ignore(80, '\n');
}
cout << "Here first" << endl;
if (first == "sp") {
You're comparing the value of the pointers (ie. comparing the memory
address locations). Use std::strcmp from <cstring> (same as strcmp
from string.h).
cout << "Here second" << endl;
Spinnerbait temp;
readInASpinnerb ait(fin);
temp.outputSpin nerbait(cout);
}
delete [] first;