I have created a program that randomly assigns roles(jobs) to members of a certain house using file input / output.. It builds successfully, but when using cout and I actually see the results, I can see why the program is not working.
Here is the snippet of code I believe something is wrong with :
std::string foo = std::string("Preferences/") + std::to_string(members[random]) + "-Preferences";
cout << foo << endl;
And here is the members[random] array, it is randomly selecting members from this array and reviewing their available times and assigning them jobs based on their Preference input file.
unsigned const char members[22] =
{ 'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v' };
I have created a random number picker that goes through 0-21 and assigns the value it creates to variable random. So, in essence, it is members[random] and completely random.
Here is the output I get in my terminal.
Preferences/116-Preferences
But I set the output to do Preferences/ member[random] -Preferences.
It is accessing a number and not my array chars.
I created a cout << members[random]; right below it, and every time I run the program, I get
Preferences/107-Preferences <---- A random number every time
k <---- random letter every time.
So I know it must be accessing my random functions, but assigned it to numbers! How do I fix this so my proper output can be :
Preferences/t-Preferences
Please help me, and thanks!
"The more you overthink the plumbing, the easier it is to stop up
the drain" - Scotty, Star Trek III
Declaring members to be unsigned chars does not accomplish anything useful. A simple char will suffice. std::string already implements an overloaded + operator that takes a char parameter, so it's much easier than you thought it would be:
const char members[22] = {
'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v' };
// ...
std::string foo = std::string("Preferences/") + members[random]
+ "-Preferences";
There is no ::std::to_string(char), only (among less close) ::std::to_string(int). So your character is actually converted to its numerical representation and you get your unwanted result.
Try instead
std::string foo("Preferences/");
foo = foo.append(1, members[random]).append("-Preferences");
Variant using string streams:
ostringstream oss;
oss << "Preferences/" << members[random] << "-Preferences";
// get your string via:
oss.str();
Related
I have some literal strings which I want to convert to integer and even double. The base is 16, 10, 8, and 2.
At this time, I wonder about the behavior of std::from_chars() - I try to convert and the error code inside from_chars_result return holds success - even if it isn't as shown here:
#include <iostream>
#include <string_view>
#include <charconv>
using namespace std::literals::string_view_literals;
int main()
{
auto const buf = "01234567890ABCDEFG.FFp1024"sv;
double d;
auto const out = std::from_chars(buf.begin(), buf.end(), d, std::chars_format::hex);
if(out.ec != std::errc{} || out.ptr != buf.end())
{
std::cerr << buf << '\n'
<< std::string(std::distance(buf.begin(), out.ptr), ' ') << "^- here\n";
auto const ec = std::make_error_code(out.ec);
std::cerr << "err: " << ec.message() << '\n';
return 1;
}
std::cout << d << '\n';
}
gives:
01234567890ABCDEFG.FFp1024
^- here
err: Success
For convenience also at coliru.
In my use case, I'll check the character set before but, I'm not sure about the checks to make it bulletproof. Is this behavior expected (maybe my English isn't sufficient, or I didn't read carefully enough)? I've never seen such checks on iterators on blogs etc.
The other question is related to different base like 2 and 8. Base of 10 and 16 seems to be supported - what would be the way for the other two bases?
Addendum/Edit:
Bulletproof here means that I can have nasty things in the string. The obvious thing for me is that 'G' is not a hex character. But I would have expected an appropriate error code in some way! The comparison out.ptr != buf.end() I've never seen in blogs (or I didn't read the right ones :)
If I enter a crazy long hex float, at least a numerical result out of range comes up.
By bulletproof I also mean that I can find such impossible strings by length, for example, so that I can save myself the call to from_chars() - for float/doubles and integers (here I would 'strlen' compare digits10 from std::numeric_limits).
The from_chars utility is designed to convert the first number it finds in the string and to return a pointer to the point where it stopped. This allows you to parse strings like "42 centimeters" by first converting the number and then parsing the rest of the string yourself for what comes after it.
The comparison out.ptr != buf.end() I've never seen in blogs (or I didn't read the right ones :)
If you know that the entire string should be a number, then checking that the pointer in the result points to the end of the string is the normal way to ensure that from_chars read the entire string.
The problem asks to create a program that asks the user to enter some text and that text will be surrounded by asterisks depending on the width of the screen for example if the user inputs "Hello world" the output should be:
****************
* Hello World! *
****************
I've tried to create the functions but I'm stuck becaus of a compiler error with the shown minimal code.
Question: Why does it tell me no matching function for within_width(text, 80)?
Some of the code I have is below:
#include <iostream>
#include <string>
void display_header (std::string &header) {
std::string text;
header = text;
}
bool within_width (std::string& text, unsigned short int& max_width) {
}
int main() {
std::string text;
std::cout << "Please enter header text: ";
std::getline(std::cin, text);
if (within_width(text, 80)) {
// call the display_header function and pass in the text
// inputted by the user
} else {
std::cout << text;
}
return 0;
}
This declaration of the function
bool within_width (std::string& text, unsigned short int& max_width)
asks for an unsigned short int variable, because it has a reference parameter, see the second &.
To satisfy it, you need to put the value 80 into a variable and give the variable as parameter.
unsigned short int MyWidth=80;
if (within_width(text, MyWidth))
Alternatively (but I assume you are not allowed) you can use a call by value parameter
bool within_width (std::string& text, unsigned short int max_width)
Then you could call as shown.
I won't give a full answer to the exercise here, just some clues.
the display_header() and within_width() functions need to know the string given in parameters but may not modify it ; thus the type of this parameter should be const std::string & (the const was missing).
the second parameter of the within_width() function is just an integer that will be compared to the length of the string ; you don't need to pass it by reference (or at least const), rather by value. Here, the (non-const) reference prevents from passing the literal constant 80.
(it seems to be the main concern of the question after edition)
You need to reason step by step.
all of this depends on the size of the string (12 for Hello World!) ; this information is available via size(text) (or text.size())
(https://en.cppreference.com/w/cpp/iterator/size)
(https://en.cppreference.com/w/cpp/string/basic_string/size)
This size will have to be compared to max_width
Displaying the line with header will require 4 more characters because * will be prepended and * will be appended.
Thus the two surrounding lines will have the length size(header)+4 too.
In order to create such a string made of *, you could use a constructor of std::string taking two parameters : the count of characters and the character to be repeated.
(https://en.cppreference.com/w/cpp/string/basic_string/basic_string)
Send all of this to std::cout in the correct order.
Edit: Just noticing that this answer probably goes far beyond the scope of the task you have been given (just filling in some skeleton that has been provided by your teacher).
I'll still leave it here to illustrate what could be done with arbitrary input. Maybe you want to experiment a little further than what you have been asked...
bool within_width(...)
Pretty simple: string.length() <= max – just wait a second, you need to consider asterisks and spaces at beginning and end of output, so: max - 4
But you can do better, you can split the string, best at word boundaries. That's a bit difficult more difficult, though:
std::vector<std::string> lines;
// we'll be starting with an initially empty line:
auto lineBegin = text.begin();
auto lineEnd = text.begin();
for(auto i = text.begin(); i != text.end(); ++)
// stop condition empty: we'll stop from inside the loop...
{
// ok, we need to find next whitespace...
// we might try using text.find_first_of("..."), but then we
// need to know any whitespace characters ourselves, so I personally
// would rather iterate manually and use isspace function to determine;
// advantage: we can do other checks at the same time, too
auto distance = std::distance(lineBegin, i);
if(std::distance(lineBegin, i) > maxLineLength)
{
if(lineEnd == lineBegin)
{
// OK, now we have a problem: the word itself is too long
// decide yourself, do you want to cut the word somewhere in the
// middle (you even might implement syllable division...)
// or just refuse to print (i. e. throw an exception you catch
// elsewhere) - decide yourself...
}
else
{
lines.emplace_back(lineBegin, lineEnd);
lineBegin = lineEnd; // start next line...
}
}
// OK, now handle current character appropriately
// note: no else: we need to handle the character in ANY case,
// if we terminated the previous line or not
if(std::isspace(static_cast<unsigned char>(*i)))
{
lineEnd = i;
}
// otherwise, we're inside a word and just go on
}
// last line hasn't been added!
lines.emplace_back(lineBegin, lineEnd);
Now you can calculate maximum length over all the strings contained. Best: Do this right when adding a new line to the vector, then you don't need a separate loop...
You might have noticed that I didn't remove whitespace at the end of the strings, so you wouldn't need to add you own one, apart, possibly, from the very last string (so you might add a lines.back() += ' ';).
The ugly part, so far, is that I left multiple subsequent whitespace. Best is removing before splitting into lines, but be aware that you need to leave at least one. So:
auto end = text.begin();
bool isInWord = false; // will remove leading whitespace, if there is
for(auto c : text)
{
if(std::isspace(static_cast<unsigned char>(c)))
{
if(isInWord)
{
*end++ = ' '; // add a single space
isInWord = false;
}
}
else
{
*end++ = c;
isInWord = true;
}
}
This would have moved all words towards the beginning of the string, but we yet to drop the surplus part of the string yet contained:
text.erase(end, text.end());
Fine, the rest is pretty simple:
iterate over maximum length, printing a single asterisk in every loop
iterate over all of your strings in the vector: std::cout << "* " << line << "*\n";
repeat the initial loop to print second line of asterisks
Finally: You introduced a fix line limit of 80 characters. If console is larger, you just won't be using the entire available width, which yet might be acceptable, if it is smaller, you will get lines broken at the wrong places.
You now could (but that's optional) try to detect the width of the console – which has been asked before, so I won't go any deeper into.
Final note: The code presented above is untested, so no guarantee to be bugfree!
I am working on city generation for a pcg game of mine. I have a for loop which makes 3 cities in random locations, I assign parentIteration to get that "id" for the city and do the same in the for loop where I make a building
for (int i = 0; i < 3; i++)
{
parentIteration = i;
std::srand(i);
_rootNode = GameManager::getSingletonPtr()->getSceneManager()->getRootSceneNode();
_cityNode = _rootNode->createChildSceneNode("cityNode " + parentIteration);
generateCity(std::rand() % 10000 + 10, std::rand() % 10000 + 10, std::rand() % 11 +1);
}
building
for (int i = 0; i < _numberOfBuildings; i++)
{
childIteration = i;
printf(" parent %d and child %d \n", parentIteration, childIteration);
Ogre::SceneNode* buildingNode = _cityNode->createChildSceneNode("citybuildingNode"+childIteration+parentIteration );
}
However when I try to launch the game it will crash on creating the second city. Saying it already has a name similar to what it is trying to write. Yet my printf clearly show that the numbers at that point are all unique. Anyone know how to resolve this issue? (added picture for proof of output)
The "itybuildingNode" in the error message suggests that
"citybuildingNode"+childIteration+parentIteration
is not working quite the way you wanted.
This is because of a couple things working against you:
"citybuildingNode" is a String Literal, and not a string object. It is litteraly just a bunch of characters in a row terminated by a null character and represented as a const char *, a pointer to that array of characters. It is low-level voodoo, the sort of stuff you might make a string class around. For more information see String Literals
Because it's not a string object, you can't pull any of the usual string object tricks like concatenating with a + and comparing with ==. But because it is a pointer, the compiler interprets + as an attempt to perform pointer arithmetic and reference another location in the array. It compiles, but note how it turned "citybuildingNode" into "itybuildingNode". Oops.
What this looks like is something like:
const char* temp = "citybuildingNode"
_cityNode->createChildSceneNode(temp + childIteration + parentIteration);
which resolves to
const char* temp = "citybuildingNode"
_cityNode->createChildSceneNode(&temp[childIteration + parentIteration]);
Even if it was a string object, the C++ standard string object, std::string does not allow you to add numbers to strings. It only adds strings together to build a bigger string. To add a number to a std::string, you have to turn the number into a std::string. std::to_string can help you here, but there is a cleaner-looking way to do this with std::stringstream
Eg:
std::stringstream nodename("citybuildingNode");
// builds a string stream around the string literal
nodename << childIteration << parentIteration;
// writes the numbers into the stream the same way `cin << number;` would
// turning the number into a string for you
Ogre::SceneNode* buildingNode = _cityNode->createChildSceneNode(nodename.str());
// gets the assembled string from the stringstream
// null-terminated string like ogre expects
This gets you started in the right direction, but still allows for collision between child 1 and parent 10 ("citybuildingNode110") and child 11 and parent 0 (also "citybuildingNode110") and similar. So you really want something more like
nodename << childIteration << '_' << parentIteration;
to force a separator between the two numbers.
Documentation for std::stringstream.
There is also another possible nasty. The string we just supplied to ogre will only exist for as long as std::stringstream nodename exists and it will die at the end of the loop that generates it. I do not see anything in a quick perusal of the documentation that says ogre makes its own copy of this string. So play around a bit to make sure that you don't have to store this name somewhere to prevent it from falling out of scope, being destroyed, and leaving ogre with a dangling reference.
I'll be flat out honest, this is a small snippet of code I need to finish my homework assignment. I know the community is very suspicious of helping students, but I've been racking my head against the wall for the past 5 hours and literally have accomplished nothing on this assignment. I've never asked for help on any assignments, but none have given me this much trouble.
All I'm having trouble with is getting the program to strip the leading whitespace out. I think I can handle the rest. I'm not asking for a solution to my overall assignment, just a nudge on this one particular section.
I'll post the full assignment text here, but I am NOT posting it to try to get a full solution, I'm only posting it so others can see the conditions I have to work with.
"This homework will give you more practice in writing functions and also how numbers are read into a variable. You need to write a function that will read an unsigned integer into a variable of type unsigned short int. This will have a maximum value of 65535, and the function needs to take care of illegal numbers. You can not use "cin >>", inside the function.
The rules for numeric input are basically as follows:
1) skip all leading white spaces
2) first character found must be numeric else an error will occur
3) numeric characters are then processed one at a time and combine with number
4) processing stops when non-numeric found
We will follow these rules and also add error handling and overflow. If an illegal entry is made before a numeric than an error code of "1" will be sent back, if overflow occurs, that is number bigger then 65535, then error code of "2" will be sent back. If no error then "0" is sent back.
Make sure the main function will continue to loop until the user enters a “n” or “N” for NO, the main should test the error code returned from the function called “ReadInt” and display appropriate error messages or display the number if there is no error. Take care in designing the “ReadInt” function, it should be value returning and have a reference parameter. The function needs to process one character at a time from the input buffer and deal with it in a correct fashion. Once the number has been read in, then make sure the input buffer is empty, otherwise the loop in main may not work correct. I know this is not how the extraction works, but lets do it this way.
You do not need to turn in an algorithm with this assignment, but I would advise you to write one. And the debugger may prove helpful as well. You are basically rewriting the extraction operator as it works on integers."
A majority of my code won't make sense as I've been deleting things and adding things like crazy to try everything I can think of.
#include <iostream>
#include <CTYPE.h>
using namespace std;
int ReadInt (unsigned short int &UserIn);
int main()
{
int Error;
unsigned short int UserInput;
char RepeatProgram;
do
{
Error=ReadInt(UserInput);
if (Error==0)
cout << "Number is " << UserInput << endl;
else if (Error==1)
cout << "Illegal Data Entry\n";
else if (Error==2)
cout << "Numerical overflow, number too big\n";
cout << "Continue? n/N to quit: ";
cin >> RepeatProgram;
cout << endl;
} while (RepeatProgram!='N' && RepeatProgram!='n');
}
int ReadInt (unsigned short int &UserIn)
{
int Err=0;
char TemporaryStorage;
long int FinalNumber=0;
cout << "Enter a number: ";
//cin.ignore(1000, !' '); this didn't work
cin.get(TemporaryStorage);
cout << TemporaryStorage;//I'm only displaying this while I test my ideas to see if they are working or not, before I move onto the the next step
cout << endl;
return Err;
}
I really appreciate any help I may get and hope I don't give the impression that I'm looking for a full free solution to the whole problem. I want to do this on my own, I'm just lot on this beginning.
As a preface, I want to state that this is a question made by a student, but unlike most of their type, it is a quality question that merits a quality answer, so I'll try to do it ;). I won't try to just answer your concrete question, but also to show you other slight problems in your code.
First of all, let's analyze your code step by step. More or less like what a debugger would do. Take your time to read this carefully ;)...
#include <iostream>
#include <CTYPE.h>
Includes headers <iostream> and <ctype.h> (the uppercase works because of some flaws/design-decisions of NTFS in Windows). I'ld recommend you to change the second line to #include <cctype> instead.
using namespace std;
This is okay for any beginner/student, but don't get an habit of it! For the purposes of "purity", I would explicitly use std:: along this answer, as if this line didn't existed.
int ReadInt (unsigned short int &UserIn);
Declares a function ReadInt that takes a reference UserIn to type unsigned short int and returns an object of type int.
int main()
{
Special function main; no parameters, returns int. Begin function.
int Error;
unsigned short int UserInput;
char RepeatProgram;
Declares variables Error, UserInput, and RepeatProgram with respective types int, unsigned short int, and char.
do
{
Do-while block. Begin.
Error=ReadInt(UserInput);
Assign return value of ReadInt of type int called with argument UserInput of type int& to variable Error of type unsigned short int.
if (Error==0)
std::cout << "Number is " << UserInput << endl;
If Error is zero, then print out UserInput to standard output.
else if (Error==1)
std::cout << "Illegal Data Entry\n";
else if (Error==2)
std::cout << "Numerical overflow, number too big\n";
Otherwise, if an error occurs, report it to the user by means of std::cout.
std::cout << "Continue? n/N to quit: ";
std::cin >> RepeatProgram;
Query the user if he/she wants to continue or quit. Store the input character in RepeatProgram of type char.
std::cout << std::endl;
Redundant, unless you want to add padding, which is probably your purpose. Actually, you're better off doing std::cout << '\n', but that doesn't matters too much.
} while (RepeatProgram!='N' && RepeatProgram!='n');
Matching expression for the do-while block above. Repeat execution of the given block if RepeatProgram is neither lower- or uppercase- letter N.
}
End function main. Implicit return value is zero.
int ReadInt (unsigned short int &UserIn)
{
Function ReadInt takes a reference UserIn to unsigned short int and returns an object of type int. Begin function.
int Err=0;
char TemporaryStorage;
long int FinalNumber=0;
Declares variables Err, TemporaryStorage, and FinalNumber of respective types int, char, and long int. Variables Err and FinalNumber are initialized to 0 and 0, respectively. But, just a single thing. Didn't the assignment said that the output number be stored in a unsigned short int? So, better of this...
unsigned short int FinalNumber = 0;
Now...
std::cout << "Enter a number: ";
//std::cin.ignore(1000, !' '); this didn't work
Eh? What's this supposed to be? (Error: Aborting debugger because this makes no logic!**). I'm expecting that you just forgot the // before the comment, right? Now, what do you expect !' ' to evaluate to other than '\0'? istream::ignore(n, ch)will discard characters from the input stream until either n characters have been discarded, ch is found, or the End-Of-File is reached.
A better approach would be...
do
std::cin.get(TemporaryStorage);
while(std::isspace(TemporyStorage));
Now...
std::cin.get(TemporaryStorage);
This line can be discarded with the above approach ;).
Right. Now, where getting into the part where you obviously banged your head against all solid objects known to mankind. Let me help you a bit there. We have this situation. With the above code, TemporaryStorage will hold the first character that is not whitespace after the do-while loop. So, we have three things left. First of all, check that at least one digit is in the input, otherwise return an error. Now, while the input is made up of digits, translate characters into integers, and multiply then add to get the actual integer. Finally, and this is the most... ahem... strange part, we need to avoid any overflows.
if (!std::isdigit(TemporaryStorage)) {
Err = 1;
return Err;
}
while (std::isdigit(TemporaryStorage)) {
unsigned short int OverflowChecker = FinalNumber;
FinalNumber *= 10; // Make slot for another digit
FinalNumber += TemporaryStorage - '0'; '0' - '0' = 0, '1' - '0' = 1...
// If an unsigned overflows, it'll "wrap-around" to zero. We exploit that to detect any possible overflow
if (FinalNumber > 65535 || OverflowChecker > FinalNumber) {
Err = 2;
return Err;
}
std::cin.get(TemporaryStorage);
}
// We've got the number, yay!
UserIn = FinalNumber;
The code is self-explanatory. Please comment if you have any doubts with it.
std::cout << TemporaryStorage;//I'm only displaying this while I test my ideas to see if they are working or not, before I move onto the the next step
cout << endl;
return Err;
Should I say something here? Anyway, I already did. Just remember to take that std::couts out before showing your work ;).
}
End function ReadInt.
You can skip leading whitespace from a stream using std::ws. For example:
std::cin >> std::ws;
This use of >> just invokes the manipulator std::ws on the stream. To meet the teacher's requirements you can invoke it directly:
std::ws(std::cin);
Formatted input automatically skips whitespace. Note that should also always check whether input was successful:
if (std::cin.get(TemporaryStorage)) {
...
}
Currently I only know of two methods to insert values into a C++ string or C string.
The first method I know of is to use std::sprintf() and a C-string buffer (char array).
The second method is to use something like "value of i: " + to_string(value) + "\n".
However, the first one needs the creation of a buffer, which leads to more code if you just want to pass a string to a function. The second one produces long lines of code, where a string gets interrupted every time a value is inserted, which makes the code harder to read.
From Python I know the format() function, which is used like this:
"Value of i: {}\n".format(i)
The braces are replaced by the value in format, and further .format()'s can be appended.
I really like Python's approach on this, because the string stays readable, and no extra buffer needs to be created. Is there any similar way of doing this in C++?
Idiomatic way of formatting data in C++ is with output streams (std::ostream reference). If you want the formatted output to end up in a std::string, use an output string stream:
ostringstream res;
res << "Value of i: " << i << "\n";
Use str() member function to harvest the resultant string:
std::string s = res.str();
This matches the approach of formatting data for output:
cout << "Value of i: " << i << "\n";