Vector of structs initialization

Question

I want know how I can add values to my vector of structs using the push back method  struct subject     string name    int marks    int credits       vector lt subject gt  sub    So now how can I add elements to it   I have function that initializes string name subject name to it   void setName string s1  string s2         string s6          how can i set name too sub 0  name   english   sub 1  name    math  etc    sub 0  name   s1    gives segmentation fault  so how do I use push back method     sub name push back s1     sub name push back s2     sub name push back s3     sub name push back s4      sub name push back s6        Function call  setName  english    math    physics       economics

User · Answer

You cannot access elements of an empty vector by subscript.
Always check that the vector is not empty & the index is valid while using the [] operator on std::vector.
[] does not add elements if none exists, but it causes an Undefined Behavior if the index is invalid.

You should create a temporary object of your structure, fill it up and then add it to the vector, using vector::push_back()

subject subObj;
subObj.name = s1;
sub.push_back(subObj);

User · Answer

You may also which to use aggregate initialization from a braced initialization list for situations like these    include  lt vector gt  using namespace std   struct subject       string name      int    marks      int    credits      int main         vector lt subject gt  sub           english   10  0           math      20  5             Sometimes however  the members of a struct may not be so simple  so you must give the compiler a hand in deducing its types   So extending on the above     include  lt vector gt  using namespace std   struct assessment       int   points      int   total      float percentage      struct subject       string name      int    marks      int    credits      vector lt assessment gt  assessments      int main         vector lt subject gt  sub           english   10  0                                 assessment 1 3 0 33f                                assessment 2 3 0 66f                                assessment 3 3 1 00f                                       math      20  5                                 assessment 2 4 0 50f                                         Without the assessment in the braced initializer the compiler will fail when attempting to deduce the type   The above has been compiled and tested with gcc in c  17  It should however work from c  11 and onward  In c  20 we may see the designator syntax  my hope is that it will allow for for the following       english   10  0   assessments                            1 3 0 33f                             2 3 0 66f                             3 3 1 00f                             source  http   en cppreference com w cpp language aggregate initialization

User · Answer

After looking on the accepted answer I realized that if know size of required vector then we have to use a loop to initialize every element   But I found new to do this using default structure element like following      include  lt bits stdc   h gt  typedef long long ll  using namespace std   typedef struct subject     string name    int marks    int credits   subject   int main      subject default subject    default subject name  NONE     default subject marks   0    default subject credits   0     vector  lt subject gt  sub 10 default subject              default subject to initialize      to check is it initialised   for ll i 0 i lt sub size   i          cout  lt  lt  sub i  name  lt  lt       lt  lt  sub i  marks  lt  lt       lt  lt  sub i  credits  lt  lt  endl           Then I think its good to way to initialize a vector of the struct  isn t it

User · Answer

If you want to use the new current standard  you can do so   sub emplace back   Math   70  0     or  sub push back    Math   70  0      These don t require default construction of subject

User · Answer

Create vector  push back element  then modify it as so   struct subject       string name      int marks      int credits       int main         vector lt subject gt  sub         Push back new subject created with default constructor      sub push back subject            Vector now has 1 element   index 0  so modify it      sub 0  name    english          Add a new element if you want another      sub push back subject            Modify its name and marks      sub 1  name    math       sub 1  marks   90      You cant access a vector with     until an element exists in the vector at that index  This example populates the     and then modifies it afterward

[c++] Vector of structs initialization

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