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When using C++ and all members should be initialised with the same value you can provide a constructor:
struct myStruct_s {
int myInt;
Bool_t myBool;
EventCallback_t myEventCallback;
myStruct_s() : myInt(0xABCD), myBool(FALSE), myEventCallback(NULL) { }
};
static struct myStruct_s myArray[DESIRED_ARRAY_SIZE];
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I forgot to mention, I'm programming in regular C.
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Then I know only four ways:
- Like you have done with multiple preprocessor
#if statements.
- Using weird preprocessor macros to create a loop.
- Initialising by code using a loop.
- Writing a helper program that creates a file with the relevant code lines that can then be included in a source file or even linked when declaring the struct as extern. The helper program must then be executed by the make file (or a corresponding custom build option when using an IDE) before compiling.
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One approach is to not bother; just initialize the array to what the maximum size could be and then store the actual size in a static variable.
If this isn't time critical, just do it dynamically. Or, make sure the default values is zero and do a memset early on.
In this case, they're all the same, so doing a quick loop early on solves the problem.
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#include <iostream>
#include <string>
using namespace std;
int main(){
const char *ptr = "tarun" ;
cout << name << endl ;
return 0;
}
in the above code if i assign a string literal to a const char*
Quote: const string *name = "tarun";
it prints the string but the same with string gives error that
Quote: cannot convert ‘const char’ to ‘const string
so it means any string literal is a const char (which i think is a rvalue),
but it is a collection of characters, so how is it a char ? and if it is a char then why it is called string literal ?
please explain.
Thank you.
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Tarun Jha wrote: n the above code if i assign a string literal to a const char*
Quote: const string *name = "tarun";
You may want to change it to
const string name = "tarun";
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Tarun Jha wrote: ...but it is a collection of characters, so how is it a char ?
The variable ptr is a pointer to a collection of char-acters, be it 1 or 100.
Tarun Jha wrote: ...then why it is called string literal ?
Like anything holding quotation marks apart, they are literally those characters. They haven't been modified, translated, obtained from some other place, coerced, etc. If you look inside the compiled file, you will see those characters, literally.
"One man's wage rise is another man's price increase." - Harold Wilson
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
"You can easily judge the character of a man by how he treats those who can do nothing for him." - James D. Miles
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To me you are sort of asking a strange question well outside the literal string part, so lets just check you understand some basics
First a string is class or if you want an object it has constructors, destructor and methods it isn't just an array of characters.
string - C++ Reference[^]
You can't remotely equate those two lines as anything similar, do you understand that?
So with a string class when you declare it as a const (like your commented out) what are you expecting it will do?
So you are clear you are asking for a constant pointer to an object and trying to set some literal string to that object.
This may also help understand Victors response and David deals with the literal part.
The point here is you can only create a string when it matches one of the constructor types of the class.
What constructor functions exist controls how you can create it.
Here is the examples of showing the seven standard constructor methods for the class
string::string - C++ Reference[^]
The situation with just a character array is very different
const char *ptr = "tarun";
We have a simple array of characters that can never be changed AKA they are constant
Everything from a C to a C++ compiler understands the later because it's very trivial.
In vino veritas
modified 3-Apr-18 23:11pm.
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Hi. I need to use OpenCV in some project, and I noticed that I have to compile myself OpenCV library.
So, I have downloaded the latest version from here: Releases - OpenCV library[^]
and I have generated the project file for VS2008, with CMake (using Windows 1064bit). All of these steps have been completed without any error. The problem begin when I have tried to compile the library itself ... I got a lot of errors:
...
...
45>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(356) : error C2065: 'uint_fast64_t' : undeclared identifier
45>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(358) : error C2065: 'uint_fast64_t' : undeclared identifier
45>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(393) : error C2146: syntax error : missing ';' before identifier 'cvRound64'
...
...
Of course, I have read the tutorials about compiling OpenCV, seem to be ok how I get the steps ... but the errors persist ... if you have some experience with OpenCV, could you help me ?
Thank you.
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Did you include the <stdint.h>?
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1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(189) : error C2065: 'uint_fast32_t' : undeclared identifier
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(189) : error C2146: syntax error : missing ';' before identifier 'vv'
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(189) : error C2065: 'vv' : undeclared identifier
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(190) : error C2065: 'vv' : undeclared identifier
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(314) : error C2065: 'uint_fast64_t' : undeclared identifier
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(321) : error C2065: 'uint_fast64_t' : undeclared identifier
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(331) : error C2065: 'uint_fast64_t' : undeclared identifier
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(331) : error C2146: syntax error : missing ';' before identifier 'vv'
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(331) : error C2065: 'vv' : undeclared identifier
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(331) : error C2065: 'uint_fast64_t' : undeclared identifier
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(332) : error C2065: 'vv' : undeclared identifier
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(348) : error C2065: 'uint_fast64_t' : undeclared identifier
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(352) : error C2065: 'uint_fast64_t' : undeclared identifier
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(354) : error C2065: 'uint_fast64_t' : undeclared identifier
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(356) : error C2065: 'uint_fast64_t' : undeclared identifier
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(358) : error C2065: 'uint_fast64_t' : undeclared identifier
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(393) : error C2146: syntax error : missing ';' before identifier 'cvRound64'
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(393) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>C:\Flaviu\opencv\sources\modules\core\include\opencv2/core/softfloat.hpp(393) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(46) : error C2065: 'uint8_t' : undeclared identifier
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(46) : error C2065: 'uint8_t' : undeclared identifier
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(46) : error C2143: syntax error : missing ')' before 'const'
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(46) : error C2143: syntax error : missing ')' before 'const'
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(46) : error C2059: syntax error : ')'
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(47) : error C2365: 'base64::base64_encode' : redefinition; previous definition was 'data variable'
1> c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(46) : see declaration of 'base64::base64_encode'
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(48) : error C2065: 'uint8_t' : undeclared identifier
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(48) : error C2143: syntax error : missing ')' before 'const'
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(48) : error C2059: syntax error : ')'
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(49) : error C2365: 'base64::base64_decode' : redefinition; previous definition was 'data variable'
1> c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(48) : see declaration of 'base64::base64_decode'
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(50) : error C2065: 'uint8_t' : undeclared identifier
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(50) : error C2143: syntax error : missing ')' before 'const'
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(50) : error C2059: syntax error : ')'
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(51) : error C2365: 'base64::base64_valid' : redefinition; previous definition was 'data variable'
1> c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(50) : see declaration of 'base64::base64_valid'
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(46) : error C2059: syntax error : ')'
1>..\..\..\sources\modules\core\src\softfloat.cpp(81) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>..\..\..\sources\modules\core\src\umatrix.cpp(482) : error C2039: 'data' : is not a member of 'std::vector<_Ty>'
1> with
1> [
1> _Ty=int
1> ]
1>..\..\..\sources\modules\core\src\persistence_xml.cpp(137) : error C2039: 'data' : is not a member of 'std::vector<_Ty>'
1> with
1> [
1> _Ty=char
1> ]
1>..\..\..\sources\modules\core\src\softfloat.cpp(81) : error C2146: syntax error : missing ';' before identifier 'globalDetectTininess'
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(47) : error C2365: 'base64::base64_encode' : redefinition; previous definition was 'data variable'
1> c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(46) : see declaration of 'base64::base64_encode'
1>..\..\..\sources\modules\core\src\persistence_xml.cpp(137) : error C2064: term does not evaluate to a function taking 4 arguments
1>..\..\..\sources\modules\core\src\softfloat.cpp(81) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(48) : error C2065: 'uint8_t' : undeclared identifier
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(48) : error C2143: syntax error : missing ')' before 'const'
1>..\..\..\sources\modules\core\src\softfloat.cpp(97) : error C2448: 'raiseFlags' : function-style initializer appears to be a function definition
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(48) : error C2059: syntax error : ')'
1>..\..\..\sources\modules\core\src\persistence_xml.cpp(154) : error C2064: term does not evaluate to a function taking 3 arguments
1>..\..\..\sources\modules\core\src\softfloat.cpp(119) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(49) : error C2365: 'base64::base64_decode' : redefinition; previous definition was 'data variable'
1> c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(48) : see declaration of 'base64::base64_decode'
1>..\..\..\sources\modules\core\src\softfloat.cpp(119) : error C2146: syntax error : missing ';' before identifier 'globalRoundingMode'
1>..\..\..\sources\modules\core\src\persistence_xml.cpp(163) : error C2039: 'data' : is not a member of 'std::vector<_Ty>'
1> with
1> [
1> _Ty=uchar
1> ]
1>persistence_types.cpp
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(50) : error C2065: 'uint8_t' : undeclared identifier
1>..\..\..\sources\modules\core\src\softfloat.cpp(119) : error C2086: 'const int cv::uint_fast8_t' : redefinition
1> ..\..\..\sources\modules\core\src\softfloat.cpp(81) : see declaration of 'cv::uint_fast8_t'
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(50) : error C2143: syntax error : missing ')' before 'const'
1>..\..\..\sources\modules\core\src\persistence_xml.cpp(180) : error C2039: 'data' : is not a member of 'std::vector<_Ty>'
1> with
1> [
1> _Ty=uchar
1> ]
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(50) : error C2059: syntax error : ')'
1>..\..\..\sources\modules\core\src\softfloat.cpp(119) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(51) : error C2365: 'base64::base64_valid' : redefinition; previous definition was 'data variable'
1> c:\flaviu\opencv\sources\modules\core\src\persistence.hpp(50) : see declaration of 'base64::base64_valid'
1>..\..\..\sources\modules\core\src\persistence_yml.cpp(100) : error C2039: 'data' : is not a member of 'std::vector<_Ty>'
1> with
1> [
1> _Ty=char
1> ]
1>..\..\..\sources\modules\core\src\persistence_yml.cpp(100) : error C2064: term does not evaluate to a function taking 4 arguments
1>..\..\..\sources\modules\core\src\persistence_yml.cpp(117) : error C2064: term does not evaluate to a function taking 3 arguments
1>..\..\..\sources\modules\core\src\softfloat.cpp(167) : error C2146: syntax error : missing ';' before identifier 'f32_to_i32'
and it count for ever ...
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Where should I insert this header ?
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If you are using precompiled header then in stdafx.h.
Otherwise - at the begin of the .hpp file that needs these type definitions (uint_fast64_t and so on)
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I have no experience with OpenCV but the reason for those errors is obvious.
Quote: I have generated the project file for VS2008
The int_fast and int_least types has been introduced with C++11 and are supported by Visual Studio since VS 2015 (see Standard Types[^]).
You might define them yourself as
typedef uint64_t uint_fast64_t;
You might also check if using C++11 is set somewhere in the OpenCV make file and disable that in the hope that the types are then defined somewhere.
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the following question is to be done using the concept of hierarchical inheritance
staff - > teacher, officer, typist
typist -> regular, casual
my solution is giving an Runtime error
below is my code :
#include <iostream>
#include <string>
using namespace std;
class staff {
string code, name;
public:
staff() : code(0000), name("Unknown") {}
virtual void getdata(void){
cout << "Enter employee name : " << endl;
getline(cin, name);
cout << "Enter employee code : " << endl;
cin >> code ;
}
virtual void putdata(void){
cout << "Employee name : " << name << endl
<< "Employee code : " << code << endl ;
}
};
class teacher : public staff {
string subject;
int publication;
public:
teacher() : subject("Empty"), publication(0000) {}
void getdata(void);
void putdata(void);
};
void teacher::getdata(){
staff::getdata();
cout << "Enter subject : " << endl ;
cin >> subject;
cout << "Enter total number of publications : " << endl ;
cin >> publication ;
}
void teacher::putdata(){
staff::putdata();
cout << "Subject : " << subject << endl
<< "publications : " << publication << endl;
}
class officer : public staff {
int grade;
string posting ;
public:
officer() : grade(0), posting("Unavailable") {}
void getdata(void);
void putdata(void);
};
void officer::getdata(){
staff::getdata();
cout << "Enter the grade : " << endl;
cin >> grade;
cout << "Enter the posting : " <<endl;
getline(cin, posting);
}
void officer::putdata(){
staff::putdata();
cout << "Officer Grade : " << grade << endl
<< "Officer Posting : " << posting << endl ;
}
class typist : public staff {
int speed;
float experience;
public:
typist() : speed(0), experience(0) {}
virtual void getdata(void);
virtual void putdata(void);
};
void typist::getdata(){
staff::getdata();
cout << "Enter typing speed :- (word/second) : " << endl;
cin >> speed;
cout << "Enter experience (int years) : " << endl;
cin >> experience ;
}
void typist::putdata(){
staff::putdata();
cout << "Typing speed ( words/second ) : " << speed << endl
<< "Experience ( in years ) : " << experience << endl ;
}
class casual : public typist {
double daily_wages;
public:
casual() : daily_wages(100) {}
void getdata(void);
void putdata(void);
};
void casual::getdata(){
typist::staff::getdata();
cout << "Enter the daily wage : " << endl ;
cin >> daily_wages;
}
void casual::putdata(){
typist::putdata();
cout << "Daily waged : " << daily_wages << endl ;
}
class regular : public typist {
double monthly_wage;
public:
regular() : monthly_wage(3000) {}
void getdata(void);
void putdata(void);
};
void regular::getdata(){
typist::getdata();
cout << "Enter Monthly wage : " << endl ;
cin >> monthly_wage;
}
void regular::putdata(){
typist::putdata();
cout << "Monthly wage : " << monthly_wage << endl;
}
int main(){
regular r1;
r1.getdata();
r1.putdata();
return 0;
}
i am not able to understand the following error:
Quote: terminate called after throwing an instance of 'std::logic_error'
what(): basic_string::_M_construct null not valid
This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.
Thank you
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You need to use the debugger to find out exactly where the error occurs.
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what is the error saying ?
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It's probably saying that you are trying to access some element that has not been initialised. And looking at your classes I cannot guess where is the most likely place. Although most of the code is not doing things in the best way.
As I have previously suggested to you, you need to get a book on C++ and learn it properly from beginning to end. You cannot learn it by continually posting questions.
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i am currently following "C++ The complete reference by : Herbert Schildt"
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class staff {
string code, name;
public:
staff() : code(0000), name("Unknown") {}
You have declared code as a string, but you are passing a value of 0, which is a null pointer.
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Which is what the debugger would have shown you.
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Is it possible to link a DLL in another DLL and call its functions?
How can we do that?
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Yes, it's possible, and the same way that you access the functions of any DLL. But your question is not clear, what problem are you having.
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