What is the best way to define const strings when there are separate header and source files?
For example, I have a header that only declare some enums. In that same header I would like to add string representations of those enums so that I can print them easily i.e string_representation[my_enum] for debug and error printing and so on.
If I define them in the header file, I will get a linker error for multiple definitions. If I remove the definition, then I can not define it in the source file.
I'm using multiple C++ files in one project for the first time. Both have need to include a protected (#ifndef) header file. However, when I do that, I get a multiple definition error.
From what I found from research, adding the word inline before the function fixes the error. Is this the right way to do this, and why does it work? Should I make a habbit of just declaring any function that might be used in two .cpp files as inline?
We have an assignment to produce code to gather a string of input from the user in which they are entering a date. We then have to extract parts of that string to make substrings, and display different formats for the date(I will add my code in here so you can see what I have done). It took me a long while plucking away at this to understand this part. You will see that at the end of my code I have opened a file months.txt. We were provided with a file which states months corresponding to dates. I.e. 01January 02February 03March 04April, and so on until December. Exactly how I have typed it is how it is in the file.
I understand how to open and extract what is in the file as a string. I have extracted this as a string called myMonth (as you can see in the code as well) NOW,
I am supposed to have the program search for the month in the file, matching that to the month the user has input earlier, and then use the number infront of that month. I understand the basics of using find(), and making substrings. But how on earth do you get the computer to correlate what the user has input for a month, to finding that in the file, and then using the correct number.
Here is the code I have done so far:
#include <iostream> #include <fstream> #include <string> using namespace std; int main() { string myDate; // Date input from user; string myMonth; // Input from months.txt
Are there other ways of calling a const/non-const override? I want to defined some functions in terms of others, particularly accessors which might or might not require constness- in order to not copy & paste code. This is my current solution:
difference between const and static const, more effectively. I know the basic concept of const and static but I need clear explanation of declaring "const" and "static const"
Is there any way to cast a non-const variable to const one?
I want to read variable n from file and then use it to declare array "int arr[n]", but because n is non-const, the compiler doesn't allow me to do that.
'Write a program to match the user input string with the contents of text files and give the result as to which files contain the input string. This has to be done by using finite automaton.' (Any language can be used) So basically, the user will input a string (in the command line or a gui) and "we must pass the text files to the DFA" (I'm double quoting this because it's precisely what my professor told) and then display those files which contain the string. The string can be hard-coded, ie,the user will get the output file that contains a specific string. ex: 'hello'. The problem is, I have never done any program on DFA so I'm at a loss. how to write the program. Should I read the files first and then use some 'switch' or 'goto' conditions for the DFA? Below is a code I found on the internet for simulating a DFA accepting a specific string.
Code:
s: accept = false; cin >> char; if char = "m" goto m; if char = EOF goto end; goto s; m: accept = false; cin >> char; if char = "m" goto m; if char = "a" goto a; if char = EOF goto end; goto s; }
I'm trying to calculate a series of times from start to end, and find out the duration between them, sum them up and see if they're above a certain value or not, for each particular instance.
My goal is to provide a prepared text file with time tags such as this:
And the program is able to calculate the total time relevant to each instance (instances separated by a line of '=').
Some form of number should somehow identify each instance or something similar and a text file is generated with total time printed for each instance. E.g.
Now I'm currently working on making the logic to calculate time within the ranges I'd like based on several parameters.
Are there any references I can use when it comes to working with strings in order to seek and extract these values in order to work with them? The documentation available on this website, despite being very informative, does not show practical applications of said class and I'm at a loss on how to implement the functionality.
In my project , we need to create an Array of Unicode Strings . The Array will contain 5000 Strings.
I need to write those strings to a text file which can be opened or edited with NotePad.
Normal _tfopen and fwrite are not able to create notepad compatible .txt file .. I mean the file I created is not readable with Notepad though file open mode is "w+t"
I read that Memory is allocated during definition of a variable and not during declaration. Declaration is something like,
Code: int x;
And definition is assigning some value to it. This is what my professor taught. My doubt is if memory is not allocated during declaration, then how the compiler successfully compiles and runs the following, which i had already tried.
Code: #include<stdio.h> #include<conio.h> int main() { int c; int *p=&c; printf("%x",p); getch(); return 0; }
The variable c is only declared. But the program outputs a memory address. Shouldn't it show an error?
I have an issue converting VC++6 code to VC++ 2010. The following template function definition is not allowed by the new compiler:
template <> void AFXAPI DelElems <CBrush*> ( CPen** objects, int count ) { for ( int i = 0; i < count; i++, objects++ ) if (*objects) delete *objects; }
All errors refer to the header of the template function:
- syntax error : '<' - syntax error : missing ';' before '<' - 'DelElems' : illegal use of type 'void' - unrecognizable template declaration/definition
I found way around this, but I would like to know why it shows multiple declarations.
My solution is to declare this class in function body(void LoadLevel()), just before the throw statement. But why can't I define it inside my namespace, but outside function?
how to get this bug to go away and I am stressing about it. The project im working on simulates packet sending and receiving along with ROT13 encryption of the packets. The error lies within the .cpp file anywhere that I used IPHost.
header file
#ifndef IPHOST_H #define IPHOST_H #include <string> #include <iostream> class IPHost { public: //Default constructor defaults to 0.0.0.0
[code]...
error message:
In function 'ZStorSt13_Ios_OpenmodeS_': line 11: multiple definition of 'IPHost::IPHost()' line 11: first defined here
**this error repeats for every line in the .cpp in which IPHost is used.
I want to use a const char* as a buffer. I am reading values from a file and adding them to a buffer. How to extract the values is simple enough. I am reading through a filestream, reading each character into a char pointer and progressing that char pointer every time. I have another char pointer marking the start positon
eg.
char *mychar = new char; char *char1 = new char; char *char2 = new char; const char *constchar ; char2 = char1; while(filestream.read(mychar,1) { *char1 = *mychar; ++char1; }
Then I get this problem: constchar = mychar; // const char* = char*.
Constchar does not catch all the data in other words. At some stage some data is lost due to zeros in the data.. How can I put values into a const char and get around this problem? The const char* will //only record everything up until the first zero.
I know that passing arguments by const instead of value is more efficient and allows us to avoid allocating a temporary local variable of the argument type. But is this always true? Or are there some cases when calling functions with constant arguments should be avoided? If so, is passing by pointer the most efficient way?
Code: #include<stdio.h> extern int v = 0; // Declaration and definition of an external int main(void)
[code]...
Is there any error? Why I take a warning: 'v' initialized and declared 'extern'|||=== Build finished: 0 errors, 1 warnings ===| ???
and what is the meaning of :An extern declaration that initializes a variable serves as a definition of the variable. This rule prevents multiple extern declarations from initializing a variable in different ways.
I have observed that inline functions can not be prototyped. example:
.cpp file:
inline void whatever() { cout<< "this is inline"<< endl; }
.h file, prototype inline void whatever(); //would ask for a definition
Because of this, I have have just made functions that are used in only 1 .cpp file (ever) inlined, to make it more efficient (and it has demonstrated that it is more efficient). It's worked out fine so far, but what about the scope of the definition??
Since an inline function is like a templated function, in that it can't be prototyped, how are name conflicts resolved, and what is the best practice for writing inline functions??
Example of a conflict:
//in some arbitrary header... void do_somthing(); //in .cpp file that inlcudes the header... inline void do_somthing() { cout<< "I'm doing somthing!!"<< endl; } int main() { do_somthing(); //which one?? it compiles fine though!! return 0; }
vijay13@ubuntu:~/Downloads$ g++ -o test test.cpp -I /home/vijay13/Downloads/OGDF-snapshot/include/
I am getting following error:
vijay13@ubuntu:~/Downloads$ g++ -o test test.cpp -I /home/vijay13/Downloads/OGDF-snapshot/include/ /tmp/ccPE8nCu.o: In function `main': test.cpp:(.text+0x26): undefined reference to `ogdf::Graph::Graph()' ...................... so on
I changed the name of my Invoice class to 'Application' and then it generated errors such as follows
Error9'Invoice.Invoice' does not contain a definition for 'Documents' and no extension method 'Documents' accepting a first argument of type 'Invoice.Invoice' could be found (are you missing a using directive or an assembly reference?)c:userskeildocumentsvisual studio 2013projectsinvoiceinvoicewritefile.cs1840Invoice
Error3'Invoice.Invoice' does not contain a definition for 'Run'C:UsersKeilDocumentsVisual Studio 2013ProjectsInvoiceInvoiceProgram.cs1921Invoice
I have added my classes here, lso I have added the sln to this post.
using System; using System.Collections.Generic; using System.ComponentModel;
I'm working on a personal project, where I have a database (SQLite) and a dataGridView. Now This is what I have:
public Form1() { DataSet ds = new DataSet(); SqlConnection connection = new SqlConnection(@"Data Source=testingsql2.s3db"); SqlDataAdapter SQLda = new SqlDataAdapter("Select * from User", connection); SqlCommandBuilder SQLcb = new SqlCommandBuilder(SQLda); dataGridView1.Fill(ds, "User"); //Error here dataGridView1.DataSource = ds; dataGridView1.DataMember = "User"; }
I've marked where I get the error.
And the Error description: Error 1 'System.Windows.Forms.DataGridView' does not contain a definition for 'Fill' and no extension method 'Fill' accepting a first argument of type 'System.Windows.Forms.DataGridView' could be found (are you missing a using directive or an assembly reference?)
I am unable to understand how a move constructor works in this example of code. If someone could break down the process of what is taking place and explain to me on why to use a move constructor.
Code: class MyString { MyString(MyString&& MoveSource) { if( MoveSource.Buffer != NULL ) { Buffer = MoveSource.Buffer; // take ownership i.e. 'move' MoveSource.Buffer = NULL; // set the move source to NULL i.e. free it } } };
Example from "SamsTeachYourself: C++ in One Hour a Day"
