Replace an element into a specific position of a vector

Question

I want to replace an element into a specific position of a vector  can I just use an assignment      vec1 and 2 have the same length  amp  filled in somehow vec1  vec2   vec1 i    vec2 i     insert vec2 i  at position i of vec1   or I have to use insert     vector lt sometype gt   iterator iterator   vec1 begin     vec1 insert iterator  i 1   vec2 i

User · Answer

See an example here  http   www cplusplus com reference stl vector insert  eg          vector  iterator iterator1     iterator1  vec1 begin      vec1 insert   iterator1 i   vec2 i         This means that at position  i  from the beginning it will insert the value from vec2 from position i    Your first approach was replacing the values from vec1 i  with the values from vec2 i

User · Answer

You can do that using at  You can try out the following simple example   const size t N   20  std  vector lt int gt  vec N   try       vec at N - 1    7    catch  std  out of range ex        std  cout  lt  lt  ex what    lt  lt  std  endl    assert vec at N - 1     7     Notice that method at returns an allocator type  reference  which is that case is a int amp   Using at is equivalent to assigning values like vec i          There is a difference between at and insert as it can be understood with the following example   const size t N   8  std  vector lt int gt  vec N   for  size t i   0  i lt 5  i         vec i    i   1     vec insert vec begin   2  10     If we now print out vec we will get   1 2 10 3 4 5 0 0 0   If  instead  we did vec at 2    10  or vec 2  10  we would get  1 2 10 4 5 0 0 0

User · Answer

vec1 i    vec2 i    will set the value of vec1 i  to the value of vec2 i   Nothing is inserted  Your second approach is almost correct  Instead of  i 1 you need just  i  v1 insert v1 begin   i  v2 i

[c++] Replace an element into a specific position of a vector

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