Converting from std::str to char

[Martin Pöpping]

Hello,

I´ve a problem with the follwing code lines:

string line;
ifstream myfile ("doorcoordinat es.txt");
if (myfile.is_open ())
{
char str[100];
char * pch;
getline (myfile,line);
str=line;
pch = strtok (str,";");
while (pch != NULL)
{
pch = strtok (NULL, " ,.");
}
myfile.close();
}
line:
str=line;

is the problem, because the compiler says, that he cannot convert from
std::str to char[100].
How do I convert/cast from std::str to char[100]?
Thanks a lot for help,
Martin

[Ben Pope]

Martin Pöpping wrote:

Hello,

I´ve a problem with the follwing code lines:

string line;
ifstream myfile ("doorcoordinat es.txt");
if (myfile.is_open ())
{
char str[100];
char * pch;
getline (myfile,line);
str=line;
pch = strtok (str,";");
while (pch != NULL)
{
pch = strtok (NULL, " ,.");
}
myfile.close();
}
line:
str=line;

is the problem, because the compiler says, that he cannot convert from
std::str to char[100].
How do I convert/cast from std::str to char[100]?

strtok takes a const char *, so don't set up all the temporary
variables, just do this:

pch = strtok (line.c_str()," ;");

Ben Pope
--
I'm not just a number. To many, I'm known as a string...

[Marchello]

>...

line:
str=line;
...
is the problem, because the compiler says, that he cannot convert from
std::str to char[100].

sprintf(str, "%s", line.c_str());

Maybe it's little wrong for "plain" C++,
but it works.

[Rolf Magnus]

Ben Pope wrote:

strtok takes a const char *,
No, it doesn't.
so don't set up all the temporary
variables, just do this:

pch = strtok (line.c_str()," ;");

This shouldn't compile.

[Martin Pöpping]

Rolf Magnus wrote:

strtok takes a const char *,

No, it doesn't.

so don't set up all the temporary
variables, just do this:

pch = strtok (line.c_str()," ;");

This shouldn't compile.

Yes you´re right. The error message is now:

'strtok' : cannot convert parameter 1 from 'const char *' to 'char *'

[David Harmon]

On Sun, 08 Jan 2006 16:32:48 +0100 in comp.lang.c++, Martin Pöpping
<ma******@despa mmed.com> wrote,

Hello,

I´ve a problem with the follwing code lines:

string line;
ifstream myfile ("doorcoordinat es.txt");
if (myfile.is_open ())
{
char str[100];

Yes, your problem is the char[100]. You forgot about using
std::string throughout and fall back to char arrays. Where the heck
did that magic 100 come from anyway? How do you know that the
"correct" value is not 98 or 101 instead?

Instead, look for an approach along the lines of:
http://groups.google.com/gr*********....earthlink.net

[David Harmon]

>Yes, your problem is the char[100]. You forgot about using

std::string throughout

I should have added, your code is easily patched up by changing
str=line;
to
strcpy(str, line.c_str());

but that would be a bad way to go for the reasons given.

[Ben Pope]

Rolf Magnus wrote:

Ben Pope wrote:

strtok takes a const char *,

No, it doesn't.

Correct.

so don't set up all the temporary
variables, just do this:

pch = strtok (line.c_str()," ;");

This shouldn't compile.

Correct.

My bad for not trying it, and instead relying on the following reference:
http://www.cplusplus.com/ref/cstring/strtok.html

The text does describe that it modifies the string.

Apologies.

Ben Pope
--
I'm not just a number. To many, I'm known as a string...

[David Harmon]

On Sun, 8 Jan 2006 18:26:02 +0200 in comp.lang.c++, "Marchello"
<ma*******@rt f-15.ntu-kpi.kiev.ua> wrote,

sprintf(str, "%s", line.c_str());

Oh, too bad you pay the cost for the heavier sprintf instead of the
lightweight strcpy, and then forget to take advantage of the one
benefit it gives you:

sprintf(str, "%99s", line.c_str());

[red floyd]

David Harmon wrote:

On Sun, 08 Jan 2006 16:32:48 +0100 in comp.lang.c++, Martin Pöpping
<ma******@despa mmed.com> wrote,

Hello,

I´ve a problem with the follwing code lines:

string line;
ifstream myfile ("doorcoordinat es.txt");
if (myfile.is_open ())
{
char str[100];

Yes, your problem is the char[100]. You forgot about using
std::string throughout and fall back to char arrays. Where the heck
did that magic 100 come from anyway? How do you know that the
"correct" value is not 98 or 101 instead?

Instead, look for an approach along the lines of:
http://groups.google.com/gr*********....earthlink.net

even better than using char[100], which is a magic number, use a
vector<char>:

while (getline(myfile ,line))
{
vector<char> buf(line.begin( ), len.end());
buf.push_back(' \0');
for (char *pch = strtok(&buf[0],";");
pch = strtok(0, " ,.");)
{
}
}