Thread: ios::noreplace (File I/O)

One result from a search on the term ios::noreplace.

Code:

ifstream blah;
if(!(blah.open("blah.txt")))
{
blah blah();
}

ERROR:
blah.cpp(33): error C2171: '!' : illegal on operands of type 'void'
aslo:
blah.cpp(33): error C2451: conditional expression of type 'void' is illegal
Expressions of type void cannot be converted to other types


The error tells you exactly what is going on. The return type of the open file stream member function is type void. You can't perform a logical not (!) on a type void. It doesn't make any sense. This is what the messages are telling you.

Try using the is_open member function instead:

Code:

ifstream blah;
blah.open("blah.txt");
if(!blah.is_open())
{
blah blah();
}

Or this (a little bit of a shortcut):

Code:

ifstream blah("blah.txt");
if(!blah.is_open())
{
blah blah();
}

It doesn't work for some reason!
The file is there but it still executes the code in the if statement!
also when i try to write from file to a string it doesn't do anything

Code:

string str, str1;
ifstream blah("blah.txt");
blah >> str1 >> str2;
cout << str1 << str2;

Content of 'blah.txt':
Text1
Text2

But when i run it nothin shows up?

Always check for success when doing input or opening a file:

Code:

ifstream blah("blah.txt")

if (!blah) {
  std::cerr<<"Error opening file\n";
  // Do something, probably terminate
}

If you get the error then the most likely problem is that the file isn't where the program is looking for it. And if the file can't be opened, the stream is not in a good state, therefore any attempt to read from it will do nothing.

Thanks guys

Just last question (I know, sorry)

Why doesn't the ifstreammembers accept strings?
or the string.c_str()?

Is there anyway to use a strings with the ifstream members?

How do i store everything in the file in 1 string?

string mystring; <--- mystring is a class object

whereas

char mycstring[42]; <--- is just an array of characters



so when you do stuff like

Code:

  myifstream.open(mystring);    // open( ) doesn't know / isn't prototyped to accept a string class variable 

.open( ) is expecting a null terminated array of characters.. A string class variable can normally simulate this using overloaded <<, >>, =, +=, [], and == operators. But on occasions where a function is expecting a null terminated character array, you can call the c_str( ) funtion from your derived string class variable and it will return a pointer to a null terminated character array.

So it's just a matter of one object being a class object vs. one being a simple array

>> Why doesn't the ifstreammembers accept strings? or the string.c_str()?
It does accept the result of .c_str(). If it isn't working for you, post the code and error.

Also, make sure you #include <string> for the string class. If you were trying to use ios::noreplace from <fstream.h> you might have incorrectly been trying to use <string.h>.