Trying to read the whole text file - c++

Question

I'm trying to read the whole contain of the txt file, not line by line, but the whole contain
and print it on screen inside a textfield in xcode
i'm using a mix of obj-c and c++ lang:
while(fgets(buff, sizeof(buff), in)!=NULL){
cout << buff; // this print the whole output in the console
NSString * string = [ NSString stringWithUTF8String:buff ] ;
[Data setStringValue:string]; // but this line only print last line inside the textfield instead of printing it all
}
I'm trying to print the whole contain of the file like:
something...
something...
etc...
but instead it just printing the last line to the textfield, please help me

Answer 1

Is there a reason you aren't using Obj-C to read the file? It would be as simple as:
NSData *d = [NSData dataWithContentsOfFile:filename];
NSString *s = [[[NSString alloc] initWithData:d encoding:NSUTF8StringEncoding] autorelease];
[Data setStringValue:s];
Edit: To use the code you have now I would try something like this:
while(fgets(buff, sizeof(buff), in)!=NULL){
NSMutableString *s = [[Data stringValue] mutableCopy];
[s appendString:[NSString stringWithUTF8String:buff]];
[Data setStringValue:s];
}

Answer 2

Read a file, return the content as a C++ string:
// open the file
std::ifstream is;
is.open(fn.c_str(), std::ios::binary);
// put the content in a C++ string
std::string str((std::istreambuf_iterator<char>(is)),
std::istreambuf_iterator<char>());
In your code you are using the C api (FILE* from cstdio). In C, the code is more complex:
char * buffer = 0; // to be filled with the entire content of the file
long length;
FILE * f = fopen (filename, "rb");
if (f) // if the file was correctly opened
{
fseek (f, 0, SEEK_END); // seek to the end
length = ftell (f); // get the length of the file
fseek (f, 0, SEEK_SET); // seek back to the beginning
buffer = malloc (length); // allocate a buffer of the correct size
if (buffer) // if allocation succeed
{
fread (buffer, 1, length, f); // read 'length' octets
}
fclose (f); // close the file
}

Answer 3

To answer the question of why your solution didn't work:
[Data setStringValue:string]; // but this line only print last line inside the textfield instead of printing it all
Assuming that Data refers to a text field, setStringValue: replaces the entire contents of the field with the string you passed in. Your loop reads and sets one line at a time, so at any given time, string is one line from the file.
Views only get told to display when you're not doing anything else on the main thread, so your loop—assuming that you didn't run it on another thread or queue—does not print one line at a time. You read each line and replace the text field's contents with that line, so when your loop finishes, the field is left with the last thing you set its stringValue to—the last line from the file.
Slurping the entire file at once will work, but a couple of problems remain:
Text fields aren't meant for displaying multiple lines. No matter how you read the file, you're still putting its contents in a place that isn't designed for such contents.
If the file is large enough, reading it will take a significant amount of time. If you do this on the main thread, then, during that time, the app will be hung.
A proper solution would be:
Use a text view, not a text field. Text views are built to work with text of any number of lines, and when you create one in a nib, it comes wrapped in a scroll view for free.
Read the file one line or other limited-size chunk at a time, but not in a for or while loop. Use NSFileHandle or dispatch_source, either of which will call a block you provide whenever they read another chunk of the file.
Append each chunk to the text view's storage instead of replacing the entire text with it.
Show a progress indicator when you start reading, then hide it when you finish reading. For extra credit, make it a determinate progress bar, showing the user how far you've gotten through the file.