What does '&' mean in C++? -

what '&' mean in c++? within function

void read_wav::read_wav(const string &filename) {  } 

and it's equivalent in c?

thanks

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edit 1

if want transform above c++ function c function, how it?

in context, & makes variable reference.

usually, when pass variable function, variable copied , function works on copy. when function returns, original variable unchanged. when pass reference, no copy made , changes made function show after function returns.

c doesn't have references, c++ reference functionally same pointer in c. difference pointers have dereferenced when use them:

    *filename = "file.wav"; 

but references can used though original variable:

    filename = "file.wav"; 

ostensibly, references supposed never null, although it's not impossible happen.

the equivalent c function be:

     void read_wav(const char* filename)      {       } 

this because c doesn't have string. usual practice in c send pointer array of characters when need string. in c++, if type string constant

    read_wav("file.wav"); 

the type const char*.