can we convert Audio (.mp3) to video (mp4) in android studio? how? - android-studio

i am new in this and i am working on App of media player and recording app. in which i have shown song list of device in the listview and recording start / stop / play. Now i want to convert that .mp3 recorded file into .mp4 and one image will show on behalf of a video in that file. Help me to achive this i have no idea and i refer many links and i didnt find anything.

Please check this link for your first question:
Why can't we initialize class members at their declaration?
Usually constructor is use to initialize value to data variables of class.
For 2nd Question:
If data member is not initialize after creation of object, It will contain garbage value. So initialize or assign suitable value to as per your need.
Check below code:
#include<iostream>
using namespace std;
class swap_values
{
int a, b, temp;
public:
swap_values(){
a=0;b=0;temp=0;
}
swap_values(int x, int y){
a = x;
b = y;
temp = 0;
}
void swapped()
{
temp = b;
b=a;
a=temp;
}
void print(){
cout<<"a: "<<a<<" b: "<<b<<endl;
}
};
int main()
{
int x =10; int y = 20;
swap_values obj(x, y);
obj.print();
obj.swapped();
obj.print();
return 0;
}

Everything can be done in better ways but just using your code this will work for you -
#include <iostream>
using namespace std;
class Swap {
private:
int a,b,temp;
public:
Swap()
{
a=10;
b=20;
temp=0;
}
void swapNums()
{
temp=a; a=b; b=temp;
cout<<a<<" " <<b<<endl;
}
};
int main() {
Swap s;
s.swapNums();
return 0;
}
You can avoid using class name as some function name. You can instead use constructor without a return type where you can initialise the member variables. swap method looks fine.

i am not able to initialize my variable in class.
class swap
{
int a=10; \\cannot declare here
int b=20; \\ cannot declare here
}
Since C++11, this is fine, you can have default member initialization.
The error is due to missing semicolon after }.
why it has garbage value with b ??
a=b;
b=temp;
temp=a;
Since temp was never initialized before assigning it to b, temp has an indeterminate value.
Any usage will lead to undefined behavior.
Here's a simple Swap struct:
struct Swap
{
int a = 10; // default member initialization
int b = 20; // default member initialization
Swap(int a = 20, int b = 10): a(b), b(a) {}; // swap on initialization
// using member initializer list
};
Swap s;
std::cout << s.a // 20
<< s.b // 10
<< std::endl;
In this example, default member initialization is "obsolete" / "redundant" due to member initializer list.

Related

how to pass structure to QT thread

Am trying to pass data structure to QT thread and but no success.
here is what am doing and have done.
i prepare data for the thread, like this and then tried to pass prepared data to thread before starting.
void mytable::prepare_data(){
// get table row count
int rowCount = ui->my_table_view->rowCount();
// create structure array based on rowCount
pnp_com_info pnp_data[rowCount];
/* pnp_com_info structure defined it top of file below includes to make it global
struct pnp_com_info{
QString com_name = "";
int x = 0;
int y = 0;
int angle = 0;
bool status = false;
};
*/
// loop on table rows columns and load pnp_data with data of columns
// PROBLEM : how to pass pnp_data structure to thread side ?
// can pass basic vars like
RunJobThread->mynum = 10;
// start QT thread
RunJobThread->start();
// std:: thread experiment
// std::stdthreadtest(pnp_data,rowCount);
}
run_job_thread.h source code
#ifndef RUN_JOB_THREAD_H
#define RUN_JOB_THREAD_H
#include <QObject>
#include <QThread>
class run_job_thread : public QThread
{
Q_OBJECT
public:
run_job_thread();
void run();
int mynum;
struct pnp_com_info_thread{
QString com_name = "";
int x = 0;
int y = 0;
int angle = 0;
bool status = false;
};
bool Stop; // bool to stop the job
signals:
void select_row_of_table_signal(int);
public slots:
};
#endif // RUN_JOB_THREAD_H
run_job_thread.cpp source code
#include "run_job_thread.h"
#include <QtCore>
run_job_thread::run_job_thread()
{
}
// run the thread
void run_job_thread::run(){
qDebug() << "my num passed value is : "<<this->mynum; // output : 10
// Goal : loop on pnp_data structure and emit signal to table rows
emit select_row_of_table_signal(5);
}
things i tried
instead of struct i tried to use other data containers like map, multimap, vectors but they give error , as am initializing pnp_com_info struct inside mytable::prepare_data() function based on rowCount which make it local and limited to prepare_data() function but with map,multimap,vector my plan was that they will be global and i will be able to access it from thread, however it not worked.
std::map<std::string, int,int,int> pnp_com_info; // error: too many template arguments for class template 'map'
std::multimap<std::string, int,int,int,bool> pnp_com_info; // error: too many template arguments for class template 'multimap'
std::vector<std::string, int,int,int,bool> pnp_com_info; // error: too many template arguments for class template 'vector'
i also tried std::thread which was partial success , i mean it was working ok but looks like std::thread not works with QT GUI thread as upon running app GUI will go freez although std::thread was doing its job
I would suggest to do the following, because the declaration of the
pnp_com_info pnp_data[rowCount];
is inside a context i think their lifecycle will be lost once you leave it, other problem is that it would be really "unsafe" to create this kind of arrays and then pass it from one side to another. Therefore I would create a QList and then pass either a copy or the reference to the worker thread. So
1) Create a QList pnp_data, in the public part of mytable
2) Fill all data using a for loop as follows.
3) Create another QList pnp_data or a QList *pnp_data (if you want to use a copy or a pointer)
4) Then just pass either a copy or a reference to the worker thread.
Then it should look like this:
mytable.h source code
public: QList<pnp_com_info> pnp_data;
mytable.cpp source code
void mytable::prepare_data(){
// get table row count
int rowCount = ui->my_table_view->rowCount();
// HERE YOU LOAD ALL THE VALUES TO THE LIST
for(int i = 0; i<rowCount; i++){
pnp_com_info itemToInsert;
//FILL HERE THE itemToInsert
//Insert the item inside the list.
pnp_data.append(itemToInsert);
}
// PROBLEM : how to pass pnp_data structure to thread side ?
// Either pass it as a copy
RunJobThread->pnp_data = pnp_data;
//or as a reference
QList<pnp_com_info> *pnpDataPointer = &pnp_data;
RunJobThread->pnp_data_reference = pnpDataPointer;
// start QT thread
RunJobThread->start();
// std:: thread experiment
// std::stdthreadtest(pnp_data,rowCount);
}
run_job_thread.h source code
#ifndef RUN_JOB_THREAD_H
#define RUN_JOB_THREAD_H
#include <QObject>
#include <QThread>
class run_job_thread : public QThread
{
Q_OBJECT
public:
run_job_thread();
void run();
struct pnp_com_info_thread{
QString com_name = "";
int x = 0;
int y = 0;
int angle = 0;
bool status = false;
};
QList<pnp_com_info> pnp_data; //This one if you create a copy
QList<pnp_com_info> *pnp_data_reference; //This if you want a pointer
bool Stop; // bool to stop the job
signals:
void select_row_of_table_signal(int);
public slots:
};
#endif // RUN_JOB_THREAD_H
I hope this helps.
First, don't subclass QThread to create a worker - re-read How To Really, Truly Use QThreads; The Full Explanation by Maya Posch. You will find it much more manageable to create a worker object and connect the threads started() to your worker's main method, and the worker's signals to the thread's quit() and deleteLater().
Then, it should be much more straightforward to pass your data to the worker before it's moved to the thread, or to use a signal connection if it needs to be passed when the worker is running (remember to register your structure with the meta-object system for that).

Displaying results in c++

I have a question concerning working with classes in c++. I must say I'm a beginner. For example, i have this class:
class student {
private:
char* name;
public:
int nrcrt;
student() {
name = new char[7];
name = "Anonim";
nrcrt = 0;
}
student(char* n, int n) {
this->name = new char[7];
strcpy(name, n);
nrcrt = nr;
}
~student() {
delete [] name;
}
char* get_name() {
return this->name;
}
}
void main() {
student group[3];
group[0] = student("Ana", 1);
group[1] = student("Alex", 2);
group[2] = student("Liam", 5);
for (i=0; i<3; i++) {
if (group.nrcrt[i] != 0)
cout << group[i].get_name() << Endl;
}
}
My question is why is it displaying different characters?
first of all your code is not working.
3.cpp:40:18: error: request for member ‘nrcrt’ in ‘group’, which is of non-class type ‘student [3]’
if(group.nrcrt[i]!=0)
i is also not declared.please make proper changes.
group.nrcrt[i]
should be changed to:
group[i].nrcrt
When the array is created, your default constructor is used.
When you assign to the elements, your destructor is called, deleting name.
The default constructor is assigning a literal to name, and deleting that memory has undefined behaviour.
In your default constructor, replace
name = "Anonim";
with
strcpy(name, "Anonim");
Your compiler should have warned you about the assignment.
If it didn't, increase the warning level of your compiler.
If it did, start listening to your compiler's warnings.
do not worry. C++ could look a bit scary as first but it is ok when you get into it. First, let's say that all classes it is good to start with upper case letters. Secondly, you have two constructors (default without parameters and one or more with, in our case one). Default consructor you need to declare an array of objects:
Student group[3];
The next important thing is that you then do not need the rest of the constructors in that case.
group[0]=student("Ana",1);
group[1]=student("Alex",2);
group[2]=student("Liam",5);
Remember to include ; at the end of class declaration. To put all the statements and expression throughout your interation within the same loop. Here is what I found as an errors anf fix them. Could probably have more.
class Student
{
private:
char* name;
public:
int nrcrt;
Student()
{
name=new char[7];
strcpy(name, "Anonim");
nrcrt=0;
}
Student( char* n, int n)
{
this->name=new char[7];
strcpy(name, n);
nrcrt=nr;
}
~Student()
{
delete [] name;
}
char* get_name()
{
return this->name;
}
};
int main()
{
Student group[3];
for(int i=0;i<3;i++)
{
if(group.nrcrt[i]!=0)
cout<<group[i].get_name()<<endl;
}
return 0;
}

VS2012 Static Analysis: this pointer as an output pointer?

In this code snippet, the Init() function acts as a on-demand initializer that fills in all member variables of the structure. This is done to avoid calling default constructors all members of a large array on the stack:
struct Foo {
int m_Member;
void Init(int i);
};
void Foo::Init(int i) {
m_Member = i;
// Many other members initialized here.
}
void SomeFunction(int n) {
Foo buffer[64];
assert(n <= 64);
// Explicitly initialize what is needed.
for (int i = 0; i < n; ++i) {
buffer[i].Init(i * 3);
}
// Use buffer[0] - buffer[n-1] somehow.
}
This triggers a static analysis error in VS2012 with /analyze:
warning C6001: Using uninitialized memory 'buffer'.: Lines: 17, 19, 20
I'm looking for a way to annotate Foo::Init() so that this warning doesn't occur. There are plenty of other ways to make the warning go away, including:
Adding an empty constructor
Moving Init() to the constructor and calling placement new in the loop
But I'd like to avoid changing the structure of the code.
I've tried the following annotation without success:
void _At_(this, _Out_) Init();
This syntax is accepted, but only changes the warning to be:
warning C6001: Using uninitialized memory 'buffer'.: Lines: 18, 20, 21
warning C6001: Using uninitialized memory 'buffer[BYTE:0]'.: Lines: 18, 20, 21
Does anyone know how I can declare the intent of this Init() function to the static analysis engine?
Your question is somewhat elusive. You have shown SomeFunction taking int, but want annotation for method Init or constructor.
The warning shown is absolutely correct, assert won't hide the warning. You need to put if to check if n is greateer than 64 and reset n (or do something else, but not to loop when n>=64).
For annotation you need to use __in_bcount or similar alternative. An example:
bool SetBuffer(__in_bcount(8) const char* sBuffer);
Whichs says sBuffer is of 8 bytes (not elements).
You can read this this article for more information.
Too ugly to add an extra helper?
struct Foo {
int m_Member;
void Init(int i);
};
void Foo::Init(int i) {
m_Member = i;
// Many other members initialized here.
}
void Initialize(__in_bcount(sizeof(Foo) * n) Foo* buffer, int n) {
// Explicitly initialize what is needed.
for (int i = 0; i < n; ++i) {
buffer[i].Init(i * 3);
}
}
void SomeFunction(int n) {
Foo buffer[64];
assert(n <= 64);
Initialize(buffer, n);
// Use buffer[0] - buffer[n-1] somehow.
}
I found a work around by implementing a function to index the array. I flagged the return value as invalid so that this new function only escapes the uninitialized value check in the specific case where the return value is only used to initialize. I've only tested this in VS2017.
#define _Ret_invalid_ _SAL2_Source_(_Ret_invalid_, (), _Ret1_impl_(__notvalid_impl))
template <typename T>
_Ret_invalid_ T& UninitialzedIndex(T* pt, int index)
{
return pt[index];
}
Then, where the value is indexed, I call UninitialzedIndex instead of operator[]
void SomeFunction(int n) {
Foo buffer[64];
if (n <= 64)
return;
// Explicitly initialize what is needed.
for (int i = 0; i < n; ++i) {
UninitialzedIndex(buffer, i).Init(i * 3);
}
// Use buffer[0] - buffer[n-1] somehow.
}
Just add a default constructor (that calls Init()). What is wrong with that?
[Edit] The root problem is not how to lie to the static analyzer or your compiler. It is how to enforce that you don't leave foo in an uninitialized state. There is nothing wrong with adding a default constructor. I'd say the desire to NOT do it imposes risk.
Perhaps some client will use that poorly constructed foo class (Long after you wrote it and long after you are gone) and perhaps they will forget to call .Init() ?? What then? They will be left with data that is uninitialized.
If you are looking to enforce that rule, no amount of static analysis will help you there.
Take care of the foundation before you put on the roof.

Why aren't these arguments valid?

//Block.h
#pragma once
class Block
{
public:
CRect pos;
int num;
public:
Block(void);
~Block(void);
};
//view class
public:
Block currentState[5]; // stores the current state of the blocks
void CpuzzleView::OnDraw(CDC* pDC)
{
CpuzzleDoc* pDoc = GetDocument();
ASSERT_VALID(pDoc);
if (!pDoc)
return;
//draw the 4 blocks and put text into them
for(int i=0;i<4;i++)
{
pDC->Rectangle(currentState[i].pos);
// i'm getting an error for this line:
pDC->TextOut(currentState[i].pos.CenterPoint(), currentState[i].num);
}
pDC->TextOut(currentState[i].pos.CenterPoint(), currentState[i].num);
The error says that no instance of overloaded function CDC::TextOutW() matches the argument list . But the prototype for the function is:
CDC::TextOutW(int x, int y, const CString &str )
all i've done is that instead of the 2 points i've directly given the point object returned by CenterPoint() ... shouldn't it work?
That's because you didn't supplied arguments list correctly. Please read compiler error message carefully, it's usually helps to solve the problem.
TextOut(currentState[i].pos.CenterPoint(), currentState[i].num);
In this call you passed CPoint object and int. This is not correct, you need to pass int, int and CString (or const char* and int length).
To fix this you shall do something like this:
CString strState;
strState.Format("%d", currentState[i].num); // Or use atoi()/wtoi() functions
TextOut(currentState[i].pos.CenterPoint().x, currentState[i].pos.CenterPoint().x, strState);

How do I pass a struct by reference in WinRT Component C++/CX

I have the following in my WinRT component:
public value struct WinRTStruct
{
int x;
int y;
};
public ref class WinRTComponent sealed
{
public:
WinRTComponent();
int TestPointerParam(WinRTStruct * wintRTStruct);
};
int WinRTComponent::TestPointerParam(WinRTStruct * wintRTStruct)
{
wintRTStruct->y = wintRTStruct->y + 100;
return wintRTStruct->x;
}
But, it seems that the value of winRTStruct->y and x are always 0 inside the method, when called from C#:
WinRTComponent comp = new WinRTComponent();
WinRTStruct winRTStruct;
winRTStruct.x = 100;
winRTStruct.y = 200;
comp.TestPointerParam(out winRTStruct);
textBlock8.Text = winRTStruct.y.ToString();
What is the correct way to pass a struct by reference so it an be updated inside the method of a WinRTComponent written in C++/CX?
You cannot pass a struct by reference. All value types (including structs) in winrt are passed by value. Winrt structs are expected to be relatively small - they're intended to be used for holding things like Point and Rect.
In your case, you've indicated that the struct is an "out" parameter - an "out" parameter is write-only, its contents are ignored on input and are copied out on return. If you want a structure to be in and out, split it into two parameters - one "in" parameter and another "out" parameter (in/out parameters are not allowed in WinRT because they don't project to JS the way you expect them to project).
My co-worker helped me solve this.
In WinRT components, it seems that the best way to do this is to define a ref struct instead of a value struct:
public ref struct WinRTStruct2 sealed
{
private: int _x;
public:
property int X
{
int get(){ return _x; }
void set(int value){ _x = value; }
}
private: int _y;
public:
property int Y
{
int get(){ return _y; }
void set(int value){ _y = value; }
}
};
But this creates other problems. Now the VS11 compiler gives INTERNAL COMPILER ERROR when I try to add a method to the ref struct that returns an instance of the struct.

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