How can I iterate through a string and also know the index current position

Question

Often when iterating through a string  or any enumerable object   we are not only interested in the current value  but also the position  index   To accomplish this by using string  iterator we have to maintain a separate index   string str   Test string    string  iterator it  int index   0  for   it   str begin     it  lt  str end    it    index          cout  lt  lt  index  lt  lt   it      The style shown above does not seem superior to the  c-style    string str   Test string    for   int i   0   i  lt  str length    i          cout  lt  lt  i  lt  lt  str i        In Ruby  we can get both content and index in a elegant way    hello  split     each with index   c  i  puts    i      c       So  what is the best practice in C   to iterate through an enumerable object and also keep track of the current index

User · Answer

Since std  distance is only constant time for random-access iterators  I would probably prefer explicit iterator arithmetic   Also  since we re writing C   code here  I do believe a more C   idiomatic solution is preferable over a C-style approach   string str  Test string    auto begin   str begin     for  auto it   str begin    end   str end    it    end    it        cout  lt  lt  it - begin  lt  lt   it

User · Answer

You can use standard STL function distance as mentioned before  index   std  distance s begin    it     Also  you can access string and some other containers with the c-like interface   for  i 0 i lt string1 length   i    string1 i

User · Answer

A good practice would be based on readability  e g    string str   Test string    for  int index   0  auto it   str begin    it  lt  str end      it     cout  lt  lt  index    lt  lt   it    Or   string str   Test string    for  int index   0  auto it   str begin    it  lt  str end      it    index     cout  lt  lt  index  lt  lt   it    Or your original   string str   Test string    int index   0  for  auto it   str begin     it  lt  str end      it    index     cout  lt  lt  index  lt  lt   it    Etc  Whatever is easiest and cleanest to you   It s not clear there is any one best practice as you ll need a counter variable somewhere  The question seems to be whether where you define it and how it is incremented works well for you

User · Answer

For strings  you can use string c str   which will return you a const char   which can be treated as an array  example   const char  strdata   str c str     for  int i   0  i  lt  str length      i      cout  lt  lt  i  lt  lt  strdata i

User · Answer

I ve never heard of a best practice for this specific question  However  one best practice in general is to use the simplest solution that solves the problem  In this case the array-style access  or c-style if you want to call it that  is the simplest way to iterate while having the index value available  So I would certainly recommend that way

User · Answer

Like this        std  string s  Test string        std  string  iterator it   s begin           Use the iterator          it                 std  cout  lt  lt   index is     lt  lt  std  distance s begin    it   lt  lt  std  endl

User · Answer

I would use it-str begin   In this particular case std  distance and operator- are the same  But if container will change to something without random access  std  distance will increment first argument until it reach second  giving thus linear time and operator- will not compile  Personally I prefer the second behaviour - it s better to be notified when you algorithm from O n  became O n 2

[c++] How can I iterate through a string and also know the index (current position)?

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