logo
down
shadow

C++ passing a nested unordered_map by reference and manipulating it


C++ passing a nested unordered_map by reference and manipulating it

By : Avraz Shawkat
Date : November 22 2020, 02:42 PM
around this issue You are not passing by reference, you're passing a pointer. This is a version using reference:
code :
void myfunc2(NESTED_MAP &st)
{
    st[1][2] = 0.5; // valid, st dereferenced implicitly
}
sc->myfunc2(STable);
void myfunc2(NESTED_MAP *st)
{
    (*st)[1][2] = 0.5;

    // or, if you like:
    st->operator[](1)[2] = 0.5;
}


Share : facebook icon twitter icon
Passing a structure by reference and manipulating it

Passing a structure by reference and manipulating it


By : user1591825
Date : March 29 2020, 07:55 AM
hope this fix your issue Using the indexed approach is slightly clearer than using the pointer arithmetic, in my opinion but either works. I suspect the code the compiler generates for each is quite similar in both instances.
strdup is necessary in this instance if you're working with variables because you do not allocate memory to save your string values in in the person struct. If you'd already allocated space for those strings when either of your setters was called, strcpy (strcpy_s, preferably) would be sufficient.
Passing structures by reference to functions, manipulating them and accessing their values from the 'main'

Passing structures by reference to functions, manipulating them and accessing their values from the 'main'


By : user5686857
Date : March 29 2020, 07:55 AM
it fixes the issue I have been rewriting some of my functions to return int instead of structs so that I can do this
code :
scan_extractor(arguments* args, scan* scans)
scans = calloc(MAX,sizeof(scan));
scan_extractor(arguments* args, scan** scans)
*scans = calloc(MAX,sizeof(scan));
scan scans; 
if (scan_extractor(&args,&scans)

scan_extractor(arguments* args, scan* scans)
scans->number = counter;
Manipulating JSON object: how to reference and update nested values

Manipulating JSON object: how to reference and update nested values


By : Georgios Theocharis
Date : March 29 2020, 07:55 AM
hope this fix your issue If we ignore the comment I left and assume you have a JavaScript object. I see the following problems:
Your ids are outside of your nested object. You're using an object but you want a 'list' you can use an array for that.
code :
var data = [{ 
        color : 'red', 
        shape : 'triangle', 
        height : 100, 
        width : 45, 
        id:1
    },
    { 
        color: 'blue', 
        shape : 'square', 
        height : 75, 
        width : 67, 
        id: 2
    },
    {
        color: 'orange', 
        shape : 'circle', 
        height : 89, 
        width :24,
        id :3 
    }];
var id3 = data.filter(function(elem){
             return elem.id === 3;
          })[0];
   id3;//the third object, with id 3
var id3 = data.find(function(elem){
             return elem.id === 3;
          });
   id3;//the third object, with id 3
var id3 = (function find(arr){
              for(var i=0;i<arr.length;i++){
                  if(arr[i].id === 3){
                      return arr[i];
                  }
              }
          })(data);
id3;
unordered_map with reference as value

unordered_map with reference as value


By : TongSu
Date : March 29 2020, 07:55 AM
With these it helps map and unordered_map are fine with references, here a working example :
code :
#include <iostream>
#include <unordered_map>

using UMap = std::unordered_map<int,int&>;

int main() {
    int a{1}, b{2}, c{3};
    UMap foo { {1,a},{2,b},{3,c} };

    // insertion and deletion are fine
    foo.insert( { 4, b } );
    foo.emplace( 5, d );
    foo.erase( 4 );
    foo.erase( 5 );

    // display b, use find as operator[] need DefaultConstructible
    std::cout << foo.find(2)->second << std::endl;

    // update b and show that the map really map on it
    b = 42;
    std::cout << foo.find(2)->second << std::endl;

    // copy is fine
    UMap bar = foo; // default construct of bar then operator= is fine too
    std::cout << bar.find(2)->second << std::endl;
}
Nested passing of reference to pointer in C++

Nested passing of reference to pointer in C++


By : FAlvarado
Date : March 29 2020, 07:55 AM
Any of those help I have an application which contains instances of an class Obj with each instance identified by an ID integer as a class members. The objects are arranged as a top level object with branches of nested sub-objects stored in a std::vector like this: , In
code :
for (Obj o : ObjTree->subObj) {
    Utils::getObj(&o, ID_L, ID_R, ObjRet);
for (Obj& o : ObjTree->subObj) {
    Utils::getObj(&o, ID_L, ID_R, ObjRet);
Related Posts Related Posts :
  • Complexity analysis of loop with limited looping time
  • Boost test fails with enum classes inside namespaces
  • is this a function declaration?
  • Socket recv() one byte at a time
  • C++ Glibc Detected error. Double Free or corruption
  • OpenCV - How to write IplImage array in Mat form?
  • Qt event when anything changed on the window/screen + Screenshot
  • OpenGL Linker error, linking with uncompiled shader
  • Find 4 specific corner pixels and use them with warp perspective
  • Cin Execution Not Working (program.exe < filewithdata.txt)
  • cudaMallocManaged causes Access Violation
  • How to correctly read a value from stdin into a variable
  • Binary Search Tree Forgetting Every Node I Add
  • C++ Return Value from function not same as that value in function
  • Microsoft Visual Studio C++, OpenCV animation
  • C++ function pointer syntax. Why does (*) work but * not?
  • C++: Template class binary operator overloading - seg fault?
  • Passing buffer between two terminals (Named Pipe)
  • C++ parse sub-string to integer
  • Create stereo context for modern opengl
  • Memory leak, when using GLM
  • Get Control under cursor
  • Is this proper behavior? std::map iterator invalidation
  • 2D isometric engine - Math problems - Cube selection - diamond shape map
  • Open second window in Qt
  • Stack Overflow error with Vectors
  • Pure Virtual Friend Class
  • Object initialization syntax in C++
  • Variable undefined error
  • C++ tolower/toupper char pointer
  • Overhead with std::function
  • Is there a way to make a loop that get user input but doesn't stop if the user doesn't input anything?
  • OpenCV in cmake-based project: checking for contrib modules
  • shared_ptr vs unique_ptr uses in classes and children
  • MFC dialog Border padding changed after switching from VS2010 to 2012 or later
  • String rotator in C++ (bitwise rotation)
  • Custom sort vector of pair based on their values
  • Pointer to const overloaded member function
  • how to avoid this for-loop mess in c++?
  • Can the state of a standard C++ iostream manipulator be polled?
  • How to make sure a data type is as large as it needs to be in C++
  • Why is my first ofstream output in my else block missing the fill character?
  • Returning static/ normal arrays in recursion/another function
  • c++, why use const std::string & parameterName?
  • expression did not evaluate to a constant in C++ VS
  • Owner object that takes pre-created values ? Wrong design?
  • Cannot use Macro in a C++ constructor?
  • vector is loosing mat4 information
  • Invalid declarator before with map of struct?
  • std::initializer_list to return member variables returns incorrect values
  • Unable to use Boost + Qt in Mac
  • Passing template function and overload as function argument
  • non standard extension warning when searching in a vector of unique_ptrs
  • Qt Windows x64 build succeeds in IDE but not on the command line
  • condition_variable::wait_for method not returning - even after the timeout
  • boost::asio usage in self-contained class
  • CGAL triangulation with constraints changes points coords
  • How to resolve an ambiguous reference caused by a conflicting identifier from inline namespace
  • When UTF8 emoji character is removed from NSMutableString the conversion to std::string fails
  • XOR of two strings of 0s and 1s
  • shadow
    Privacy Policy - Terms - Contact Us © animezone.co