What is the difference between tmain and main in C

Question

If I run my C   application with the following main   method everything is OK   int main int argc  char  argv          cout  lt  lt   There are    lt  lt  argc  lt  lt    arguments    lt  lt  endl         Loop through each argument and print its number and value    for  int i 0  i lt argc  i          cout  lt  lt  i  lt  lt       lt  lt  argv i   lt  lt  endl      return 0      I get what I expect and my arguments are printed out   However  if I use  tmain   int  tmain int argc  char  argv          cout  lt  lt   There are    lt  lt  argc  lt  lt    arguments    lt  lt  endl         Loop through each argument and print its number and value    for  int i 0  i lt argc  i          cout  lt  lt  i  lt  lt       lt  lt  argv i   lt  lt  endl      return 0      It just displays the first character of each argument   What is the difference causing this

User · Answer

tmain is a macro that gets redefined depending on whether or not you compile with Unicode or ASCII   It is a Microsoft extension and isn t guaranteed to work on any other compilers   The correct declaration is   int  tmain int argc   TCHAR  argv       If the macro UNICODE is defined  that expands to  int wmain int argc  wchar t  argv      Otherwise it expands to   int main int argc  char  argv      Your definition goes for a bit of each  and  if you have UNICODE defined  will expand to    int wmain int argc  char  argv      which is just plain wrong   std  cout works with ASCII characters   You need std  wcout if you are using wide characters   try something like this   include  lt iostream gt   include  lt tchar h gt    if defined UNICODE       define  tcout std  wcout  else      define  tcout std  cout  endif  int  tmain int argc   TCHAR  argv           tcout  lt  lt   T  There are     lt  lt  argc  lt  lt   T   arguments     lt  lt  std  endl         Loop through each argument and print its number and value    for  int i 0  i lt argc  i           tcout  lt  lt  i  lt  lt   T       lt  lt  argv i   lt  lt  std  endl      return 0      Or you could just decide in advance whether to use wide or narrow characters    -   Updated 12 Nov 2013   Changed the traditional  TCHAR  to   TCHAR  which seems to be the latest fashion   Both work fine   End Update

User · Answer

With a little effort of templatizing this  it wold work with any list of objects    include  lt iostream gt   include  lt string gt   include  lt vector gt   char non repeating char std  string str       while str size    gt   2           std  vector lt size t gt  rmlist           for size t  i   1   i  lt  str size    i                         if str 0     str i                     rmlist push back i                                                    if rmlist size                             size t s   0      Need for terator position adjustment                str erase str begin     0                 s              for  size t j   rmlist                      str erase str begin      j-s                                      s                         continue                    return str 0            if str size      1  return str 0       else return -1     int main int argc  char    args        std  string test    FabaccdbefafFG       test   args 1       char non repeating   non repeating char test       Std  cout  lt  lt  non repeating  lt  lt    n

User · Answer

Ok  the question seems to have been answered fairly well  the UNICODE overload should take a wide character array as its second parameter  So if the command line parameter is  Hello  that would probably end up as  H 0e 0l 0l 0o 0 0 0  and your program would only print the  H  before it sees what it thinks is a null terminator   So now you may wonder why it even compiles and links   Well it compiles because you are allowed to define an overload to a function    Linking is a slightly more complex issue  In C  there is no decorated symbol information so it just finds a function called main  The argc and argv are probably always there as call-stack parameters just in case even if your function is defined with that signature  even if your function happens to ignore them   Even though C   does have decorated symbols  it almost certainly uses C-linkage for main  rather than a clever linker that looks for each one in turn  So it found your wmain and put the parameters onto the call-stack in case it is the int wmain int  wchar t     version

User · Answer

tmain does not exist in C    main does    tmain is a Microsoft extension   main is  according to the C   standard  the program s entry point  It has one of these two signatures   int main    int main int argc  char  argv       Microsoft has added a wmain which replaces the second signature with this   int wmain int argc  wchar t  argv       And then  to make it easier to switch between Unicode  UTF-16  and their multibyte character set  they ve defined  tmain which  if Unicode is enabled  is compiled as wmain  and otherwise as main   As for the second part of your question  the first part of the puzzle is that your main function is wrong  wmain should take a wchar t argument  not char  Since the compiler doesn t enforce this for the main function  you get a program where an array of wchar t strings are passed to the main function  which interprets them as char strings   Now  in UTF-16  the character set used by Windows when Unicode is enabled  all the ASCII characters are represented as the pair of bytes  0 followed by the ASCII value   And since the x86 CPU is little-endian  the order of these bytes are swapped  so that the ASCII value comes first  then followed by a null byte   And in a char string  how is the string usually terminated  Yep  by a null byte  So your program sees a bunch of strings  each one byte long   In general  you have three options when doing Windows programming    Explicitly use Unicode  call wmain  and for every Windows API function which takes char-related arguments  call the -W version of the function  Instead of CreateWindow  call CreateWindowW   And instead of using char use wchar t  and so on Explicitly disable Unicode  Call main  and CreateWindowA  and use char for strings  Allow both   call  tmain  and CreateWindow  which resolve to main  tmain and CreateWindowA CreateWindowW   and use TCHAR instead of char wchar t    The same applies to the string types defined by windows h  LPCTSTR resolves to either LPCSTR or LPCWSTR  and for every other type that includes char or wchar t  a -T- version always exists which can be used instead   Note that all of this is Microsoft specific  TCHAR is not a standard C   type  it is a macro defined in windows h  wmain and  tmain are also defined by Microsoft only

User · Answer

the  T convention is used to indicate the program should use the character set defined for the application  Unicode  ASCII  MBCS  etc    You can surround your strings with  T    to have them stored in the correct format    cout  lt  lt   T   There are      lt  lt  argc  lt  lt   T    arguments      lt  lt  endl

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