stl

C++ Vector at/[] operator speed

In order to give functions the option to modify the vector I can't do curr = myvec.at( i ); doThis( curr ); doThat( curr ); doStuffWith( curr ); But I have to do: doThis( myvec.at( i ) ); doThat( myvec.at( i ) ); doStuffWith( myvec.at( i ) ); (as the answers of my other question pointed out) I'm going to make a hell lot of calls ...

How to initialise a STL vector/list with a class without invoking the copy constructor

I have a C++ program that uses a std::list containing instances of a class. If I call e.g. myList.push_back(MyClass(variable)); it goes through the process of creating a temporary variable, and then immediately copies it to the vector, and afterwards deletes the temporary variable. This is not nearly as efficient as I want, and sucks whe...

for_each but for setting each element to a value in C++

I have the following code to assign a value to all the elements of a vector: x = 100; for (int i=0;i<vect.size();i++) { vect[i] = x; } It's straightforward enough, but I'm wondering if there is a function in the STL that does the same thing; something like for_each, but for assignment. ...

Best way to insert items from a Derived class's constructor into a Base class's private std::vector?

I have these classes: class Base { ... private: std::vector<X> v; }; class Derived : public Base { Derived(X*, int n); }; where the constructor of Derived is passed an array of item Xs, which I need to insert into my vector v in the Base class. (X is a smart pointer) Currently I see two ways to do this: Create a function in Base: ...

push_back of STL list got bad performance?

I wrote a simple program to test STL list performance against a simple C list-like data structure. It shows bad performance at "push_back()" line. Any comments on it? $ ./test2 Build the type list : time consumed -> 0.311465 Iterate over all items: time consumed -> 0.00898 Build the simple C List: time consumed -> 0.020275 Iterate o...

What is the best way to store incremental downloaded data?

Inspired by Chromium's sha1 class, I am thinking to store incrementally downloaded data using std::string // pseudo-code char buff[BUFF_SIZE]; std::string data; do { size = ReadInternetFileTo(buff,BUFF_SIZE); data.append(buff,size); } while (not_finished); Any foreseeable problems with this method or better way to do it? ...

Calling unmanaged c++ code in C# Mixed with STL

Hey, I want to call unmanaged c++ code in C# The function interface is like following(I simplified it to make it easy to understand) Face genMesh(int param1, int param2); Face is a struct defined as: struct Face{ vector<float> nodes; vector<int> indexs; } I googled and read the MSDN docs found ways to call simple c/c++ un...

c++ stl priority queue insert bad_alloc exception

Hi, I am working on a query processor that reads in long lists of document id's from memory and looks for matching id's. When it finds one, it creates a DOC struct containing the docid (an int) and the document's rank (a double) and pushes it on to a priority queue. My problem is that when the word(s) searched for has a long list, when ...

Idiomatic STL: Iterating over a list and inserting elements

I'm writing an algorithm that iterates over a list of points, calculates the distance between them and inserts additional points if the distance is too great. However I seem to be lacking the proper familiarity with STL to come up with an elegant solution. I'm hoping that I can learn something, so I'll just show you my code. You might ha...

What's correct way to remove a boost::shared_ptr from a list?

I have a std::list of boost::shared_ptr<T> and I want to remove an item from it but I only have a pointer of type T* which matches one of the items in the list. However I cant use myList.remove( tPtr ) I'm guessing because shared_ptr does not implement == for its template argument type. My immediate thought was to try myList.remove( sh...

std::deque: How do I get an iterator pointing to the element at a specified index?

I have a std::deque, and I want to insert an element at a specified index (I'm aware that std::list would be better at this). The deque::insert() function takes an iterator to specify the location to insert. Given an index, how can I get an iterator pointing to that location, so that I can pass that iterator to insert()? For example: ...

Containers of reference_wrappers (comparison operators required?)

If you use stl containers together with reference_wrappers of POD types, code such as the following works just fine: int i = 0; std::vector< boost::reference_wrapper<int> > is; is.push_back(boost::ref(i)); std::cout << (std::find(is.begin(),is.end(),i)!=is.end()) << std::endl; However, if you use non-POD types like (contrived example)...

operator<< cannot output std::endl -- Fix?

The following code gives an error when it's supposed to output just std::endl: #include <iostream> #include <sstream> struct MyStream { std::ostream* out_; MyStream(std::ostream* out) : out_(out) {} std::ostream& operator<<(const std::string& s) { (*out_) << s; return *out_; } }; template<class OutputStream> struct Foo...

std::map keys in C++

I have a requirement to create two different maps in C++. The Key is of type CHAR* and the Value is a pointer to a struct. I am filling 2 maps with these pairs, in separate iterations. After creating both maps I need find all such instances in which the value of the string referenced by the CHAR* are same. For this I am using the follo...

Switching from C++ (with a lot of STL use) to C for interpreter building

I'm switching from C++ to C because I'm rebuilding my toy interpreter. I was used to vectors for dynamic allocation of objects like tokens or instructions of my programs, stacks and mainly strings with all their aspects. Now, in C I'm not going to have all these anymore. I know that I will have to use a lot of memory management, too. ...

Vector [] vs copying

What is faster and/or generally better? vector<myType> myVec; int i; myType current; for( i = 0; i < 1000000; i ++ ) { current = myVec[ i ]; doSomethingWith( current ); doAlotMoreWith( current ); messAroundWith( current ); checkSomeValuesOf( current ); } or vector<myType> myVec; int i; for( i = 0; i < 1000000; i ++ ) { doSome...

Is there a standard Cyclic Iterator in C++

Based on the following question: Check if one string is a rotation of other string I was thinking of making a cyclic iterator type that takes a range, and would be able to solve the above problem like so: std::string s1 = "abc" ; std::string s2 = "bca" ; std::size_t n = 2; // number of cycles cyclic_iterator it(s2.begin(),s2.end(),n); ...

Using stack defined in C++ stl

#include <stack> using namespace std; int main() { stack<int> s; int i; for (i = 0; i <= 10; i++) { s.push(i); } for (i = 0; i <= 10; i++) { printf("%d", s.pop()); } } Whats wrong with the code above? Error: In function int main(): aggregate value used where an integer was expected ...

How to read and write a STL C++ string?

#include<string> ... string in; //How do I store a string from stdin to in? // //gets(in) - 16 cannot convert `std::string' to `char*' for argument `1' to //char* gets (char*)' // //scanf("%s",in) also gives some weird error Similarly, how do I write out in to stdout or to a file?? ...

Output iterator's value_type

The STL commonly defines an output iterator like so: template<class Cont> class insert_iterator : public iterator<output_iterator_tag,void,void,void,void> { // ... Why do output iterators define value_type as void? It would be useful for an algorithm to know what type of value it is supposed to output. For example, a function tha...