<vector> and new

[jacek]

Hi I'm trying to do this (and it seem works):

std::vector<Light*> light; // it's a vector of pointer to Light
Light* l;
l = new Light[10];
light.push_back(l);
delete [] l; //delete is necessary

std::vector<Light*> light; // it's a vector of pointer to Light
Light* l;
l = new Light[10];
light.push_back(l);
delete [] l; //delete is necessary

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Here you use that vector as if it was a vector of arrays, but there is one problem --- if you delete the "l" pointer, the pointer you have appended to the vector will be invalid, because it will point to a deleted array.

It should be:

std::vector<Light*> light;
Light* l;
l = new Light[10];
light.push_back(l);
 
// ... use light ...
 
// delete the contents of light vector
for( std::vector<Light*>::iterator i = light.begin(); i != light.end(); ++i ) {
   delete [] *i;
}
lisht.clear();

std::vector<Light*> light;
Light* l;
l = new Light[10];
light.push_back(l);

// ... use light ...

// delete the contents of light vector
for( std::vector<Light*>::iterator i = light.begin(); i != light.end(); ++i ) {
   delete [] *i;
}
lisht.clear();

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Otherwise:

std::vector<Light*> light; // it's a vector of pointer to Light
Light* l;
l = new Light;
for (int i=0; < 10< i++)
     light.push_back(l);
delete [] l; //delete is necessary

std::vector<Light*> light; // it's a vector of pointer to Light
Light* l;
l = new Light;
for (int i=0; < 10< i++)
     light.push_back(l);
delete [] l; //delete is necessary

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Here you use the same variable as if it was a vector of pointers to Light instance, but again there is a problem --- all elements point to the same instance, if you delete it, all pointers in the vector will be invalid.

std::vector<Light*> light; // it's a vector of pointer to Light
 
for (int i=0; < 10< i++) {
     Light* l = new Light();
     light.push_back(l);
     // or simply:
     // light.push_back( new Light() );
}
 
// ... use light ...
 
// delete the contents of light vector
for( std::vector<Light*>::iterator i = light.begin(); i != light.end(); ++i ) {
   delete *i; // note no []
}
lisht.clear();

std::vector<Light*> light; // it's a vector of pointer to Light

for (int i=0; < 10< i++) {
     Light* l = new Light();
     light.push_back(l);
     // or simply:
     // light.push_back( new Light() );
}

// ... use light ...

// delete the contents of light vector
for( std::vector<Light*>::iterator i = light.begin(); i != light.end(); ++i ) {
   delete *i; // note no []
}
lisht.clear();

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Another problem is that you can't use delete[] to free memory allocated with new --- always use the same kind of operator: delete after new and delete [] after new[].

Here I've a vecotr of 10 elements (pointer) that each one point to a Light;

std::vector<Light> light;
for (int i=0; <10; i++) 
    light.push_back(Light());

std::vector<Light> light;
for (int i=0; <10; i++) 
    light.push_back(Light());

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I prefer the last....
Wich is better?

This is the safest way to use a vector.

Note that you can achieve the same with this:

std::vector<Light> light;
light.resize( 10 );
// or even
// std::vector<Light> light( 10 );

std::vector<Light> light;
light.resize( 10 );
// or even
// std::vector<Light> light( 10 );

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It will fill the vector with 10 copies of Light().