I'm following a book and currently learning about pointers and such however when i run this code i also get a wierd error sound. It's kinda cool that it does but i don't know why it's called and the book didn't say anything about (possibly cause the book is decently old now). The sound occurs when i call for 'ErrorMessage'. Is that some kind of easter egg cause i don't remember including any audio libaries?
#include <iostream>
ErrorMessage(char* msg)
{
std::cout << "\aError:" << msg << std::endl;
}
int main()
{
char* ep = "Invalid Input";
ErrorMessage(ep);
char msg[] = "Disk Failure";
ErrorMessage(msg);
ErrorMessage("Timeout");
}
You have used an escape sequence when you've typed that backslash in your std::cout literal.
\a is a very old-fashioned way of sending a beep signal to your terminal (called the BEL character), assuming your console (i.e. the thing that you used to launch your application) supports beeping.
\a (the a stands for alert)is the encoding for the ASCII BEL character, which will cause the terminal bell to be rung when it is output, assuming your terminal software or hardware supports such functionality.
Its because of
std::cout << "\aError:" << msg << std::endl;
Notice that \a.
\a is an escape character which is audible alert which is generating that sound
\a is the control character for a bell sound, so printing it to std::cout will produce one; exactly what ErrorMessage() does:
std::cout << "\aError:" << msg << std::endl; // make a beep then print "Error: <msg>"
Related
I'm using Visual Studio 2019: why does this command do nothing?
std::cout << unsigned char(133);
It literally gets skipped by my compiler (I verified it using step-by-step debug):
I expected a print of à.
Every output before the next command is ignored, but not the previous ones. (std::cout << "12" << unsigned char(133) << "34"; prints "12")
I've also tried to change it to these:
std::cout << unsigned char(133) << std::flush;
std::cout << (unsigned char)(133);
std::cout << char(-123);
but the result is the same.
I remember that it worked before, and some of my programs that use this command have misteriously stopped working... In a blank new project same result!
I thought that it my new custom keyboard layout could be the cause, but disabling it does not change so much.
On other online compilers it works properly, so may it be a bug of Visual Studio 2019?
The "sane" answer is: don't rely on extended-ASCII characters. Unicode is widespread enough to make this the preferred approach:
#include <iostream>
int main() {
std::cout << u8"\u00e0\n";
}
This will explicitly print the character à you requested; in fact, that's also how your browser understands it, which you can easily verify by putting into e.g. some unicode character search, which will result in LATIN SMALL LETTER A WITH GRAVE, with the code U+00E0 which you can spot in the code above.
In your example, there's no difference between using a signed or unsigned char; the byte value 133 gets written to the terminal, but the way it interprets it might differ from machine to machine, basing on how it's actually set up to interpret it. In fact, in a UTF-8 console, this is simply a wrong unicode sequence (u"\0x85" isn't a valid character) - if your OS was switched to UTF-8, that might be why you're seeing no output.
You can try to use static_cast
std::cout << static_cast<unsigned char>(133) << std::endl;
Or
std::cout << static_cast<char>(133) << std::endl;
Since in mine all of this is working, it's hard to pinpoint the problem, the common sense would point to some configuration issue.
Normally c/cpp string displayed in console only allows user to type after it.
Is there any simple way to let user to type in the middle of the output string, e.g fill in the blank:
Mr ____ is the teacher.
std::cout can print it easily, but how to let user type directly in the blank with simple code and read it? And e.g. if the name is long the move the printed character to the right?
You're looking for controlling a console/terminal. Neither of the languages you ask about has any notion of that -- they both only know streams of input and output. This is a simple abstraction, input and output are done character by character, in sequence. Input doesn't have to come from a keyboard, output doesn't have to be a screen or terminal ...
Controlling the contents of a screen is very platform-dependent. If you are on windows, the windows API provides a bunch of functions for controlling a console.
If you want to do something cross-platform, have a look at curses. There are implementations for many platforms, like ncurses (often used on *nix systems) and pdcurses (which is quite good for windows) and they all provide the same interface.
To learn about curses programming, the NCURSES Programming HOWTO is a good start. Just replace #include <ncurses.h> with #include <curses.h> so your code isn't tied specifically to ncurses but works with any curses implementation.
Yes, you can absolutely do this (I mean, ever played snake? All games were on terminals back then, and your problem is much simpler than writing a game).
A trick is using \r, which is a carriage return. That character will slide you back to the start of the line, allowing you to overwrite the previous string. This is commonly used for loading animations like
[---]
[=---]
[==-]
[===]
To prevent forcing the user to hit enter before sending data, I'll show a Linux/Mac solution.
system("/bin/stty raw"); // Get keystrokes immediately, #include <stdlib.h>
string s;
char c;
cout << "Mr _ is the teacher." << flush;
while( c = getchar() ) { // #include <stdio.h>
if( c == 3 ) // CTRL+C
exit(1);
if( c == 13 ) { // Newline
cout << endl;
break;
}
if( c == 127 ) { // Backspace
if( s.size() > 0 )
s.pop_back();
} else {
s += c;
}
cout << "\r"; // Reset the cursor
cout << "Mr " << s << "_ is the teacher. " << flush; // Spaces to cover invalid backspace character
cout << "\r"; // Reset the cursor
cout << "Mr " << s << "_ is the teacher." << flush;
}
system("/bin/stty cooked"); // Go back to buffered input
This can be done in Windows by importing #include<conio.h>, and then using getch() instead of getchar(). (You don't need any stty system commands)
Make sure to use your platform-specific #ifdef's to make your code portable!
I was wondering what is the most efficient performant way to output a new line to console. Please explain why one technique is more efficient. Efficient in terms of performance.
For example:
cout << endl;
cout << "\n";
puts("");
printf("\n");
The motivation for this question is that I find my self writing loops with outputs and I need to output a new line after all iterations of the loop. I'm trying to find out what's the most efficient way to do this assuming nothing else matters. This assumption that nothing else matters is probably wrong.
putchar('\n') is the most simple and probably fastest. cout and printf with string "\n" work with null terminated string and this is slower because you process 2 bytes (0A 00). By the way, carriage return is \r = 13 (0x0D). \n code is Line Feed (LF).
You don't specify whether you are demanding that the update to the screen is immediate or deferred until the next flush. Therefore:
if you're using iostream io:
cout.put('\n');
if you're using stdio io:
std::putchar('\n');
The answer to this question is really "it depends".
In isolation - if all you're measuring is the performance of writing a '\n' character to the standard output device, not tweaking the device, not changing what buffering occurs - then it will be hard to beat options like
putchar('\n');
fputchar('\n', stdout);
std::cout.put('\n');
The problem is that this doesn't achieve much - all it does (assuming the output is to a screen or visible application window) is move the cursor down the screen, and move previous output up. Not exactly a entertaining or otherwise valuable experience for a user of your program. So you won't do this in isolation.
But what comes into play to affect performance (however you measure that) if we don't output newlines in isolation? Let's see;
Output of stdout (or std::cout) is buffered by default. For the output to be visible, options include turning off buffering or for the code to periodically flush the buffer. It is also possible to use stderr (or std::cerr) since that is not buffered by default - assuming stderr is also directed to the console, and output to it has the same performance characteristics as stdout.
stdout and std::cout are formally synchronised by default (e.g. look up std::ios_base::sync_with_stdio) to allow mixing of output to stdout and std::cout (same goes for stderr and std::cerr)
If your code outputs more than a set of newline characters, there is the processing (accessing or reading data that the output is based on, by whatever means) to produce those other outputs, the handling of those by output functions, etc.
There are different measures of performance, and therefore different means of improving efficiency based on each one. For example, there might be CPU cycles, total time for output to appear on the console, memory usage, etc etc
The console might be a physical screen, it might be a window created by the application (e.g. hosted in X, windows). Performance will be affected by choice of hardware, implementation of windowing/GUI subsystems, the operating system, etc etc.
The above is just a selection, but there are numerous factors that determine what might be considered more or less performance.
On Ubuntu 15.10, g++ v5.2.1 (and an older vxWorks, and OSE)
It is easy to demonstrate that
std::cout << std::endl;
puts a new line char into the output buffer, and then flushes the buffer to the device.
But
std::cout << "\n";
puts a new line char into the output buffer, and does not output to the device. Some future action will be needed to trigger the output of the newline char in the buffer to the device.
Two such actions are:
std::cout << std::flush; // will output the buffer'd new line char
std::cout << std::endl; // will output 2 new line chars
There are also several other actions that can trigger the flush of the std::cout buffering.
#include <unistd.h> // for Linux
void msDelay (int ms) { usleep(ms * 1000); }
int main(int, char**)
{
std::cout << "with endl and no delay " << std::endl;
std::cout << "with newline and 3 sec delay " << std::flush << "\n";
msDelay(3000);
std::cout << std::endl << " 2 newlines";
return(0);
}
And, per comment by someone who knows (sorry, I don't know how to copy his name here), there are exceptions for some environments.
It's actually OS/Compiler implementation dependent.
The most efficient, least side effect guaranteed way to output a '\n' newline character is to use std::ostream::write() (and for some systems requires std::ostream was opened in std::ios_base::binary mode):
static const char newline = '\n';
std::cout.write(&newline,sizeof(newline));
I would suggest to use:
std::cout << '\n'; /* Use std::ios_base::sync_with_stdio(false) if applicable */
or
fputc('\n', stdout);
And turn the optimization on and let the compiler decide what is best way to do this trivial job.
Well if you want to change the line I'd like to add the simplest and the most common way which is using (endl), which has the added perk of flushing the stream, unlike cout << '\n'; on its own.
Example:
cout << "So i want a new line" << endl;
cout << "Here is your new line";
Output:
So i want a new line
Here is your new line
This can be done for as much new lines you want. Allow me to show an example using 2 new lines, it'll definitely clear all of your doubts,
Example:
cout << "This is the first line" << endl;
cout << "This is the second line" << endl;
cout << "This is the third line";
Output:
This is the first line
This is the second line
This is the third line
The last line will just have a semicolon to close since no newline is needed. (endl) is also chain-able if needed, as an example, cout << endl << endl; would be a valid sequence.
I've been using Vim a lot lately, and I was wondering how the program manages to change the characters at certain positions in the terminal. For example, when using :rc, it replaces the character under the cursor with c.
I have also seen similar things done with Homebrew, which prints a progress bar to the screen and updates it when necessary.
How is this done in C/C++?
There is no standard way of doing this in C++.
It is done with OS dependent lbiraries, such as curses and similar libraries (ncurses) in the Unix/Linux world. Some of these libraries have been ported on across platforms (example: PDCurses)
For very simple things such as a progress bar or a counter, and as long as you remain on a single line there is the trick of using "\r" (carriage return) in the output, to place the cursor back at the begin of the current line. Example:
for (int i = 0; i < 100; i++) {
cout << "\rProgress: " << setw(3) << i;
this_thread::sleep_for(chrono::milliseconds(100));
}
Certainly, using ncurses or similar library is a good answer. An alternative may be to use ANSI Escape Codes to control the cursor in some terminal emulators (but not Windows command shell). For example, this code prints a line in multiple colors and then moves the cursor to 2,2 (coordinates are 1-based with 1,1 being the upper left corner) and prints the word "red" in the color red.
#include <iostream>
#include <string>
const std::string CSI{"\x1b["};
const std::string BLUE{CSI + "34m"};
const std::string RED{CSI + "31m"};
const std::string RESET{CSI + "0m"};
std::ostream &curpos(int row, int col)
{
return std::cout << CSI << row << ';' << col << 'H';
}
int main()
{
std::cout << "This is " << BLUE << "blue" << RESET << " and white.\n";
curpos(2,2);
std::cout << RED << "red" << RESET << '\n';
}
As mentioned that's not a matter of any C/C++ standard operations provided with stdout or cout (besides writing the necessary control characters to the screen).
Controlling the screen cursor of an ASCII terminal totally depends on implementation of the particular terminal program used, and besides a very narrow set of control characters, there's no standard established.
There are libraries like ncurses for a broader variety of linux terminal implementations, or PDcurses for a windows CMD shell.
I'm not sure to understand you completely but with creating an array of 100 elements of type char you can modify any position of the array and loop it with a std:cout to mostrate it on the console.
Perhaps could be better define the array of 50 chars to resuce the size of the printed result.
For example, if you have to print a progessbar in the 1% process, you should print:
Char progressbar[100] = {'X','','','','','','','','',........}
The Problem
I'm developing an 32 bit unmanaged application in C++ on Windows using Visual Studio 2010. Forgive my lack of Windows knowledge as I usually develop on *nix.
Initially, in my program my calls to std::cout's stream insertion operator work fine. For example, the following statement outputs as expected:
std::cout << "hello" << std::endl;
However, the following code does not work:
std::cout << "\thello" << std::endl;
...call to DLL from Japanese company who won't respond to support requests...
std::cout << "\thello" << std::endl;
The above code prints:
hello
(inverted diamond symbol)hello(eighth note music symbol)(inverted o symbol)
Once I have called this DLL for the first time my output to std::cout is forever messed up. The symbols that are printed are not found in an ASCII table. The inverted o symbol is a single unicode char that looks like the letter 'o' but the black part of the o is white, and the white part is black(inverted colors). The music symbol is the unicode 8th note character.
Any ideas on why this is happening and how to fix it? It seems that this DLL is messing up how control characters (chars starting with \) are outputted.
What I have tried so far
I thought this might be a locale issue since the DLL is from a Japanese company. However, after the DLL call the locale is still "C" just as it was before the call. I use the following to query the locale:
printf ("Locale is: %s\n", setlocale(LC_ALL,NULL) );
I also thought this might be some kind of bizarre memory corruption but it seems that the \r\n gets replaced by (music symbol)(inverted o) whereas \t gets replaced by an inverted diamond symbol. There seems to be a regular "replace A by B" pattern for all the control chars, which would not indicate memory corruption.
Lastly, I also tried this:
std::cout << "blah" << '\r' << '\n';
and I see the same garbage characters created by:
std::cout << "blah" << std::endl;
Thanks in advance for any help and insight.
See whether this fixes it:
#include <iostream>
#include <locale>
int main()
{
std::cout << "\thello" << std::endl;
// ...call to DLL from Japanese company who won't respond to support requests...
locale mylocale(""); // or "C" // Construct locale object with the user's default preferences
std::cout.imbue( mylocale ); // Imbue that locale
std::cout << "\thello" << std::endl;
return 0;
}
Consult the documentation for that library whether
the change of locale is by design
it can be configured otherwise
You could perhaps associate another stream with cout
std::ostream cout2;
cout2.rdbuf(std::cout.rdbuf());
And use it. I'm sure that won't be thread safe. Flushing might be 'awkward' - but it should work