What is stdcall

Question

I m learning about Win32 programming  and the WinMain prototype looks like   int WINAPI WinMain   HINSTANCE instance  HINSTANCE prev instance  PSTR cmd line  int cmd show     I was confused as to what this WINAPI identifier was for and found    define WINAPI        stdcall   What does this do   I m confused by this having something at all after a return type   What is   stdcall for   What does it mean when there is something between the return type and function name

User · Accepted Answer

stdcall is the calling convention used for the function   This tells the compiler the rules that apply for setting up the stack  pushing arguments and getting a return value   There are a number of other calling conventions    cdecl    thiscall    fastcall and the wonderfully named   declspec naked      stdcall is the standard calling convention for Win32 system calls    Wikipedia covers the details   It primarily matters when you are calling a function outside of your code  e g  an OS API  or the OS is calling you  as is the case here with WinMain    If the compiler doesn t know the correct calling convention then you will likely get very strange crashes as the stack will not be managed correctly

User · Answer

It has to do with how the function is called- basically the order in which things are put on the the stack and who is responsible for cleanup   Here s the documentation  but it doesn t mean much unless you understand the first part  http   msdn microsoft com en-us library zxk0tw93 aspx

User · Answer

C or C   itself do not define those identifiers  They are compiler extensions and stand for certain calling conventions  That determines where to put arguments  in what order  where the called function will find the return address  and so on  For example    fastcall means that arguments of functions are passed over registers   The Wikipedia Article provides an overview of the different calling conventions found out there

User · Answer

stdcall is used to put the function arguments in the stack  After the completion of the function it automatically deallocates the memory  This is used for fixed arguments   void   stdcall fnname   int  int                 int main         CreateThread   NULL  0  fnname  int  int              Here the fnname has args it directly push into the stack

User · Answer

I agree that all the answers so far are correct  but here is the reason   Microsoft s C and C   compilers provide various calling conventions for  intended  speed of function calls within an application s C and C   functions   In each case  the caller and callee must agree on which calling convention to use   Now  Windows itself provides functions  APIs   and those have already been compiled  so when you call them you must conform to them   Any calls to Windows APIs  and callbacks from Windows APIs  must use the   stdcall convention

User · Answer

It has to do with how the function is called- basically the order in which things are put on the the stack and who is responsible for cleanup   Here s the documentation  but it doesn t mean much unless you understand the first part  http   msdn microsoft com en-us library zxk0tw93 aspx

User · Answer

I agree that all the answers so far are correct  but here is the reason   Microsoft s C and C   compilers provide various calling conventions for  intended  speed of function calls within an application s C and C   functions   In each case  the caller and callee must agree on which calling convention to use   Now  Windows itself provides functions  APIs   and those have already been compiled  so when you call them you must conform to them   Any calls to Windows APIs  and callbacks from Windows APIs  must use the   stdcall convention

User · Answer

Have a look at   http   www codeproject com KB cpp calling conventions demystified aspx

User · Answer

C or C   itself do not define those identifiers  They are compiler extensions and stand for certain calling conventions  That determines where to put arguments  in what order  where the called function will find the return address  and so on  For example    fastcall means that arguments of functions are passed over registers   The Wikipedia Article provides an overview of the different calling conventions found out there

User · Answer

I agree that all the answers so far are correct  but here is the reason   Microsoft s C and C   compilers provide various calling conventions for  intended  speed of function calls within an application s C and C   functions   In each case  the caller and callee must agree on which calling convention to use   Now  Windows itself provides functions  APIs   and those have already been compiled  so when you call them you must conform to them   Any calls to Windows APIs  and callbacks from Windows APIs  must use the   stdcall convention

User · Answer

Have a look at   http   www codeproject com KB cpp calling conventions demystified aspx

User · Answer

The answers so far have covered the details  but if you don t intend to drop down to assembly  then all you have to know is that both the caller and the callee must use the same calling convention  otherwise you ll get bugs that are hard to find

User · Answer

The answers so far have covered the details  but if you don t intend to drop down to assembly  then all you have to know is that both the caller and the callee must use the same calling convention  otherwise you ll get bugs that are hard to find

User · Answer

C or C   itself do not define those identifiers  They are compiler extensions and stand for certain calling conventions  That determines where to put arguments  in what order  where the called function will find the return address  and so on  For example    fastcall means that arguments of functions are passed over registers   The Wikipedia Article provides an overview of the different calling conventions found out there

User · Answer

C or C   itself do not define those identifiers  They are compiler extensions and stand for certain calling conventions  That determines where to put arguments  in what order  where the called function will find the return address  and so on  For example    fastcall means that arguments of functions are passed over registers   The Wikipedia Article provides an overview of the different calling conventions found out there

User · Answer

I agree that all the answers so far are correct  but here is the reason   Microsoft s C and C   compilers provide various calling conventions for  intended  speed of function calls within an application s C and C   functions   In each case  the caller and callee must agree on which calling convention to use   Now  Windows itself provides functions  APIs   and those have already been compiled  so when you call them you must conform to them   Any calls to Windows APIs  and callbacks from Windows APIs  must use the   stdcall convention

User · Answer

The answers so far have covered the details  but if you don t intend to drop down to assembly  then all you have to know is that both the caller and the callee must use the same calling convention  otherwise you ll get bugs that are hard to find

User · Answer

stdcall is used to put the function arguments in the stack  After the completion of the function it automatically deallocates the memory  This is used for fixed arguments   void   stdcall fnname   int  int                 int main         CreateThread   NULL  0  fnname  int  int              Here the fnname has args it directly push into the stack

User · Answer

It has to do with how the function is called- basically the order in which things are put on the the stack and who is responsible for cleanup   Here s the documentation  but it doesn t mean much unless you understand the first part  http   msdn microsoft com en-us library zxk0tw93 aspx

User · Answer

I never had to use this before until today  Its because in my code I am using multi-threadding and the multi-threading API I am using is the windows one   beginthreadex    To start the thread    beginthreadex NULL  0  ExecuteCommand  currCommand  0  0     The ExecuteCommand function MUST use the   stdcall keyword in the method signature in order for beginthreadex to call it   unsigned int   stdcall Scene  ExecuteCommand void  command        return system static cast lt char  gt  command

User · Answer

I never had to use this before until today  Its because in my code I am using multi-threadding and the multi-threading API I am using is the windows one   beginthreadex    To start the thread    beginthreadex NULL  0  ExecuteCommand  currCommand  0  0     The ExecuteCommand function MUST use the   stdcall keyword in the method signature in order for beginthreadex to call it   unsigned int   stdcall Scene  ExecuteCommand void  command        return system static cast lt char  gt  command

User · Answer

The answers so far have covered the details  but if you don t intend to drop down to assembly  then all you have to know is that both the caller and the callee must use the same calling convention  otherwise you ll get bugs that are hard to find

User · Answer

It has to do with how the function is called- basically the order in which things are put on the the stack and who is responsible for cleanup   Here s the documentation  but it doesn t mean much unless you understand the first part  http   msdn microsoft com en-us library zxk0tw93 aspx

[c] What is __stdcall?

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