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  • Does cout need to be terminated with a semicolon ?

    - by Philippe Harewood
    I am reading Bjarne Stroustrup's Programming : Principles and Practice Using C++ In the drill section for Chapter 2 it talks about various ways to look at typing errors when compiling the hello_world program #include "std_lib_facilities.h" int main() //C++ programs start by executing the function main { cout << "Hello, World!\n", // output "Hello, World!" keep_window_open(); // wait for a character to be entered return 0; } In particular this section asks: Think of at least five more errors you might have made typing in your program (e.g. forget keep_window_open(), leave the Caps Lock key on while typing a word, or type a comma instead of a semicolon) and try each to see what happens when you try to compile and run those versions. For the cout line, you can see that there is a comma instead of a semicolon. This compiles and runs (for me). Is it making an assumption ( like in the javascript question: Why use semicolon? ) that the statement has been terminated ? Because when I try for keep_terminal_open(); the compiler informs me of the semicolon exclusion.

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  • What are the lengths/limits C preprocessor as a language creation tool? Where can I learn more about

    - by Weston C
    In his FAQ @ http://www2.research.att.com/~bs/bs_faq.html#bootstrapping, Bjarne Stroustrup says: To build [Cfront, the first C++ compiler], I first used C to write a "C with Classes"-to-C preprocessor. "C with Classes" was a C dialect that became the immediate ancestor to C++... I then wrote the first version of Cfront in "C with Classes". When I read this, it piqued my interest in the C preprocessor. I'd seen its macro capabilities as suitable for simplifying common expressions but hadn't thought about its ability to significantly add to syntax and semantics on the level that I imagine bringing classes to C took. So now I have a couple of questions on my mind: 1) Are there other examples of this approach to bootstrapping a language off of C? 2) Is the source to Stroustrup's original work available anywhere? 3) Where could I learn more about the specifics of utilizing this technique? 4) What are the lengths/limits of that approach? Could one, say, create a set of preprocessor macros that let someone write in something significantly Lisp/Scheme like?

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  • Sequence Point and Evaluation Order( Preincrement)

    - by Josh
    There was a debate today among some of my colleagues and I wanted to clarify it. It is about the evaluation order and the sequence point in an expression. It is clearly stated in the standard that C/C++ does not have a left-to-right evaluation in an expression unlike languages like Java which is guaranteed to have a sequencial left-to-right order. So, in the below expression, the evaluation of the leftmost operand(B) in the binary operation is sequenced before the evaluation of the rightmost operand(C): A = B B_OP C The following expression according, to CPPReference under the subsection Sequenced-before rules(Undefined Behaviour) and Bjarne's TCPPL 3rd ed, is an UB x = x++ + 1; It could be interpreted as the compilers like BUT the expression below is said to be clearly a well defined behaviour in C++11 x = ++x + 1; So, if the above expression is well defined, what is the "fate" of this? array[x] = ++x; It seems the evaluation of a post-increment and post-decrement is not defined but the pre-increment and the pre-decrement is defined. NOTE: This is not used in a real-life code. Clang 3.4 and GCC 4.8 clearly warns about both the pre- and post-increment sequence point.

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  • C++ : Declaring the array size with a non-constant variable

    - by Jérôme
    I always thought that when declaring an array in C++, the size has to be a constant integer value. For instance : int MyArray[5]; // correct or const int ARRAY_SIZE = 6; int MyArray[ARRAY_SIZE]; // correct but int ArraySize = 5; int MyArray[ArraySize]; // incorrect Here is also what is explained in The C++ Programming Language, by Bjarne Stroustrup : The number of elements of the array, the array bound, must be a constant expression (§C.5). If you need variable bounds, use a vector(§3.7.1, §16.3). For example: void f(int i) { int v1[i]; // error : array size not a constant expression vector<int> v2[i]; // ok } But to my big surprise, the code above does compile fine on my system ! Here is what I tried to compile : void f(int i) { int v2[i]; } int main() { int i = 3; int v1[i]; f(5); } I got no error ! I'm using GCC v4.4.0. Is there something I'm missing ?

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  • Jquery: how to trigger td a when tr is clicked

    - by Poku
    Hey, I have a table where the first td in the trs contains a link. I want this anchor to be triggered (clicked) no matter where i click in the containing tr. I have read and tried alot of recents post and suggentions on this topic but i can't get this to work. I tried the trigger() and triggerHandle() functions, but it does not trigger the anchor click that i want. There must be others who have had the need to trigger a anchor click when a tr is clicked, so that the user doesn't have to click the tds anchor link. It sure is a nice UI feature if its possible? Here is the code i have tried: <head> <meta http-equiv="content-type" content="text/html; charset=utf-8" /> <script type="text/javascript" src="javascripts/jquery-1.4.2.js"></script> <script type="text/javascript" charset="utf-8"> /* Initialise the table with the required column sorting data types */ jQuery(document).ready(function () { jQuery("#rowClick tr").click(function (e) { jQuery("#clickevent", this).trigger("click"); }); }); </script> </head> <body id="dt_example"> <table id="rowClick"> <thead> <tr> <th style="width: 30px">id</th> <th style="width: 200px">navn</th> </tr> </thead> <tbody> <tr> <td><a href="datatabletext.asp?test=1" id="clickevent">1</a></td> <td>Jesper</td> </tr> <tr> <td><a href="datatabletext.asp?test=2" id="clickevent">2</a></td> <td>Bjarne</td> </tr> <tr> <td><a href="datatabletext.asp?test=3" id="clickevent">3</a></td> <td>Søren</td> </tr> </tbody> </table> </body>

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