What does - mean in C

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Possible Duplicates    What is the difference between the dot     operator and - gt   in C      What is the arrow operator  - gt   synonym for in C          The header says it all   What does -  mean in C

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x- y can mean 2 things  If x is a pointer  then it means member y of object pointed to by x  If x is an object with operator-    overloaded  then it means x operator-

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a- gt b means   a  b   If a is a pointer   a- gt b is the member b of which a points to   a can also be a pointer like object  like a vector lt bool gt  s stub  override the operators    if you don t know what a pointer is  you have another question

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member b of object pointed to by a a- b

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It s to access a member function or member variable of an object through a pointer  as opposed to a regular variable or reference   For example  with a regular variable or reference  you use the   operator to access member functions or member variables   std  string s    abc   std  cout  lt  lt  s length    lt  lt  std  endl    But if you re working with a pointer  you need to use the - gt  operator   std  string  s   new std  string  abc    std  cout  lt  lt  s- gt length    lt  lt  std  endl    It can also be overloaded to perform a specific function for a certain object type   Smart pointers like shared ptr and unique ptr  as well as STL container iterators  overload this operator to mimic native pointer semantics   For example   std  map lt int  int gt   iterator it   mymap begin    end   mymap end    for    it    end    it      std  cout  lt  lt  it- gt first  lt  lt  std  endl

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http   en wikipedia org wiki Operators in C and C 2B 2B Member and pointer operators  a - gt  b is member b of object pointed to by a

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The - gt  operator  which is applied exclusively to pointers  is needed to obtain the specified field or method of the object referenced by the pointer   this applies also to structs just for their fields   If you have a variable ptr declared as a pointer you can think of it as   ptr  field   A side node that I add just to make pedantic people happy  AS ALMOST EVERY OPERATOR you can define a different semantic of the operator by overloading it for your classes

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Access operator applicable to  a  all pointer types   b  all types which explicitely overload this operator Introducer for the return type of a local lambda expression   std  vector lt MyType gt  seq     fill with instances      std  sort seq begin    seq end                    const MyType amp  a  const MyType amp  b  - gt  bool                   return a Content  lt  b Content                   introducing a trailing return type of a function in combination of the re-invented auto   struct MyType          declares a member function returning std  string     auto foo int  - gt  std  string

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