Check if element is in the list contains

Question

I ve got a list of elements  say  integers and I want to check if my variable  another integer  is one of the elements from the list  In python I d do   my list    1 2 3 4    elements my var   3   my variable my var in my list   returns boolean   How to do that in C    I thought of using std  list  but I can find no find method in it  I can see such method in std  set structure   More deeply  the problem is that my program is given some unique ids  a list  a set  whatever  and I iterate over a long list of input data  ids  and check if they are included in the list  boolean value returned for each iteration step   And I m not sure how should I do that in C

User · Answer

Declare additional helper function like this:

template <class T, class I >
bool vectorContains(const vector<T>& v, I& t)
{
    bool found = (std::find(v.begin(), v.end(), t) != v.end());
    return found;
}

And use it like this:

void Project::AddPlatform(const char* platform)
{
    if (!vectorContains(platforms, platform))
        platforms.push_back(platform);
}

Snapshot of example can be found here:

https://github.com/tapika/cppscriptcore/blob/b7f3d62747494a52a440482e841ffb016a3fc56e/SolutionProjectModel/Project.cpp#L13

User · Answer

You can use std  find  bool found    std  find my list begin    my list end    my var     my list end       You need to include  lt algorithm gt   It should work on standard containers  vectors lists  etc

User · Answer

you must  include  lt algorithm gt   then you can use std  find

User · Answer

A one-liner solution  similar to python  would be  std  set lt int gt   1  2  3  4   count my var   gt  0  Minimal working example int my var   3  bool myVarIn    std  set lt int gt   1  2  3  4   count my var   gt  0  std  cout  lt  lt  std  boolalpha  lt  lt  myVarIn  lt  lt  std  endl   prints true or false dependent of the value of my var

User · Answer

Use std  find  something like   if  std  find std  begin my list   std  end my list   my var     std  end my list          my list has my var

User · Answer

They really should add a wrapper  Like this   namespace std       template lt class  container          class  Ty gt  inline         bool contains  container  C  const  Ty amp   Val           return std  find  C begin     C end     Val      C end                 if  std  contains my container  what to find

User · Answer

std  list does not provide a search method  You can iterate over the list and check if the element exists  or use std  find  But I think for your situation std  set is more preferable  The former will take O n  time but later will take O lg n   time to search  You can simply use  int my var   3  std  set lt int gt  mySet  1  2  3  4   if mySet find myVar     mySet end             do whatever

[c++] Check if element is in the list (contains)

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