When you open a file, all kinds of things can go wrong. A file lives on a physical device — a fixed disk, for example, or perhaps on a flash drive or SD card — and you can run into problems when working with physical devices.
For example, part of the disk might be damaged, causing an existing file to become corrupted. Or, less disastrous, you might run out of disk space. Or, even less disastrous, you might try to open a file in a directory that doesn’t exist.
I havent programmed in C for about 3 years. Since i started uni actually. Now i gotta implement some stuff for Algorithms and Complexity. I've got a vague idea of how to do that but thats not my problem. According to my memory and old programs that i dug up for my hard disk the following code. The 'c' in cout refers to 'character' and 'out' means 'output', hence cout means 'character output'. The cout object is used along with the insertion operator (in order to display a stream of characters. The general syntax is: cout cout. Hellow, kevin thedevil. You cannot write simply cout, because Dev-C thinks cout is a variable.You must write the program thus: include. On Sat, 2002-07-06 at 08:09, h.roessner@. Wrote: HelloI have two questions. At first, is there intended (in near future) to build a package with fltk? I have an FLTK package on my hd, I'm just feeling too lazy to actually release it. When you open a file, all kinds of things can go wrong. A file lives on a physical device — a fixed disk, for example, or perhaps on a flash drive or SD card — and you can run into problems when working with physical devices. For example, part of the disk might be damaged, causing an existing file to become corrupted.
If you try to open a file for writing by specifying a full path and filename but the directory does not exist, the computer responds differently, depending on the operating system you’re using. If you’re unsure how your particular operating system will respond, try writing a simple test application that tries to create and open something like /abc/def/ghi/jkl/abc.txt. (Of course, you’ll want to be sure to use a directory that doesn’t exist.)
Then one of two things will happen: Either the directory and the file will get created, or nothing will happen.
For example, on a Windows system, if we attempt to create a file in a directory that doesn’t exist, the system does not create the directory. That’s because deep down inside, the application ultimately calls an operating system function that does the dirty work of creating the file. And this particular operating system function (it’s called CreateFile(), if you even care) has a rule that it will not create a directory for you.
If you want to determine whether the ostream class was unable to create a file, you can call its fail() member function. This function returns true if the object couldn’t create the file. And that’s what happens when a directory doesn’t exist. The DirectoryCheck01 example shown demonstrates an example of this.
When you run this code, assuming that you don’t have a directory called /abc/def/ghi on your system, you should see the message Couldn’t open the file! Assuming that your particular operating system doesn’t create a directory in this case; if it does, your computer will open the file, write Hi to it, and move on with its happy life after closing things out.
As an alternative to calling the fail() member function, you can use an operator available in various stream classes. This is !, fondly referred to as the “bang” operator, and you would use it in place of calling fail(), as in this code:
Most people prefer to use !outfile instead of outfile.fail(), although !outfile makes confusing code. The reason is that outfile is an object, and the notion of !outfile simply doesn’t make sense.
In fact, !outfile trips up many beginning programmers. They know that outfile is not a pointer in this sample code, and they wonder how you could test it against 0 as you normally can only do with a pointer. (Remember, by saying !x, where x is some pointer, you’re testing x against 0.) And that simply doesn’t make sense! And so, to avoid confusion, just call fail(). It makes more sense.
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Here are some reasons your file creation may choke:
- The directory doesn’t exist.
- You’re out of disk space and out of luck.
- Your application doesn’t have the right permissions to create a file.
- The filename was invalid — that is, it contained characters the operating system doesn’t allow in a filename, such as * or ?.
Like any good application, your application should do two things:
- 1.Check whether a file creation succeeded.
- 2.If the file creation failed, handle it appropriately.Don’t just print a horrible message like Oops!Aborting!, leaving your poor users with no choice but to toss the monitor onto the floor. Instead, do something friendlier — such as presenting a message telling them there’s a problem and suggesting that they might free more disk space.
- C++ Basics
- C++ Object Oriented
- C++ Advanced
- C++ Useful Resources
- Selected Reading
When we consider a C++ program, it can be defined as a collection of objects that communicate via invoking each other's methods. Let us now briefly look into what a class, object, methods, and instant variables mean.
- Object − Objects have states and behaviors. Example: A dog has states - color, name, breed as well as behaviors - wagging, barking, eating. An object is an instance of a class.
- Class − A class can be defined as a template/blueprint that describes the behaviors/states that object of its type support.
- Methods − A method is basically a behavior. A class can contain many methods. It is in methods where the logics are written, data is manipulated and all the actions are executed.
- Instance Variables − Each object has its unique set of instance variables. An object's state is created by the values assigned to these instance variables.
C++ Program Structure
Let us look at a simple code that would print the words Hello World.
Let us look at the various parts of the above program −
- The C++ language defines several headers, which contain information that is either necessary or useful to your program. For this program, the header <iostream> is needed.
- The line using namespace std; tells the compiler to use the std namespace. Namespaces are a relatively recent addition to C++.
- The next line '// main() is where program execution begins.' is a single-line comment available in C++. Single-line comments begin with // and stop at the end of the line.
- The line int main() is the main function where program execution begins.
- The next line cout << 'Hello World'; causes the message 'Hello World' to be displayed on the screen.
- The next line return 0; terminates main( )function and causes it to return the value 0 to the calling process.
Compile and Execute C++ Program
Let's look at how to save the file, compile and run the program. Please follow the steps given below −
- Open a text editor and add the code as above.
- Save the file as: hello.cpp
- Open a command prompt and go to the directory where you saved the file.
- Type 'g++ hello.cpp' and press enter to compile your code. If there are no errors in your code the command prompt will take you to the next line and would generate a.out executable file.
- Now, type 'a.out' to run your program.
- You will be able to see ' Hello World ' printed on the window.
Make sure that g++ is in your path and that you are running it in the directory containing file hello.cpp.
You can compile C/C++ programs using makefile. For more details, you can check our 'Makefile Tutorial'.
Semicolons and Blocks in C++
In C++, the semicolon is a statement terminator. That is, each individual statement must be ended with a semicolon. It indicates the end of one logical entity.
For example, following are three different statements −
A block is a set of logically connected statements that are surrounded by opening and closing braces. For example −
C++ does not recognize the end of the line as a terminator. For this reason, it does not matter where you put a statement in a line. For example −
is the same as
C++ Identifiers
Cout Error In Dev C Code
A C++ identifier is a name used to identify a variable, function, class, module, or any other user-defined item. An identifier starts with a letter A to Z or a to z or an underscore (_) followed by zero or more letters, underscores, and digits (0 to 9).
C++ does not allow punctuation characters such as @, $, and % within identifiers. C++ is a case-sensitive programming language. Thus, Manpower and manpower are two different identifiers in C++.
Here are some examples of acceptable identifiers −
C++ Keywords
The following list shows the reserved words in C++. These reserved words may not be used as constant or variable or any other identifier names.
asm | else | new | this |
auto | enum | operator | throw |
bool | explicit | private | true |
break | export | protected | try |
case | extern | public | typedef |
catch | false | register | typeid |
char | float | reinterpret_cast | typename |
class | for | return | union |
const | friend | short | unsigned |
const_cast | goto | signed | using |
continue | if | sizeof | virtual |
default | inline | static | void |
delete | int | static_cast | volatile |
do | long | struct | wchar_t |
double | mutable | switch | while |
dynamic_cast | namespace | template |
Trigraphs
A few characters have an alternative representation, called a trigraph sequence. A trigraph is a three-character sequence that represents a single character and the sequence always starts with two question marks.
Trigraphs are expanded anywhere they appear, including within string literals and character literals, in comments, and in preprocessor directives.
Tcp auto tuning windows 7. Following are most frequently used trigraph sequences −
Trigraph | Replacement |
---|---|
??= | # |
??/ | |
??' | ^ |
??( | [ |
??) | ] |
??! | | |
??< | { |
??> | } |
??- | ~ |
All the compilers do not support trigraphs and they are not advised to be used because of their confusing nature.
Whitespace in C++
A line containing only whitespace, possibly with a comment, is known as a blank line, and C++ compiler totally ignores it.
Whitespace is the term used in C++ to describe blanks, tabs, newline characters and comments. Whitespace separates one part of a statement from another and enables the compiler to identify where one element in a statement, such as int, ends and the next element begins.
Statement 1
In the above statement there must be at least one whitespace character (usually a space) between int and age for the compiler to be able to distinguish them.
![Dev Dev](/uploads/1/2/6/6/126607430/323861456.png)
Statement 2
C++ Error Type Std Cout
In the above statement 2, no whitespace characters are necessary between fruit and =, or between = and apples, although you are free to include some if you wish for readability purpose.