How to view the assembly behind the code using Visual C

Question

I was reading another question pertaining the efficiency of two lines of code  and the OP said that he looked at the assembly behind the code and both lines were identical in assembly   Digression aside  how could I view the assembly code created when a program is compiled   I m using Microsoft s Visual C    but I would also like to know if it s possible to view the assembly behind code written in Visual Basic   So  how do I view the assembly code behind a program written in higher level languages like C   and Visual Basic

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Specify the  FA switch for the cl compiler  Depending on the value of the switch either only assembly code or high-level code and assembly code is integrated  The filename gets  asm file extension  Here are the supported values       FA  Assembly code   asm  FAc     Machine and assembly code   cod  FAs     Source and assembly code   asm  FAcs    Machine  source  and assembly code   cod

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The easiest way is to fire the debugger and check the disassembly window

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For MSVC you can use the linker   link exe  dump  linenumbers  disasm  out foo dis foo dll  foo pdb needs to be available to get symbols

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Additional note  there is big difference between Debug assembler output and Release one  The first one is good to learn how compiler produces assembler code from C    The second one is good to learn how compiler optimizes various C   constructs  In this case some C  -to-asm transformations are not obvious

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Red Gate s  NET Reflector is a pretty awesome tool that has helped me out more than a few times   The plus side of this utility outside of easily showing you MSIL is that you can analyze a lot of third-party DLLs and have the Reflector take care of converting MSIL to C  and VB   I m not promising the code will be as clear as source but you shouldn t have much trouble following it

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In Visual C   the project options under  Output Files I believe has an option for outputing the ASM listing with source code   So you will see the C C   source code and the resulting ASM all in the same file

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There are several approaches    You can normally see assembly code while debugging C   in visual studio  and eclipse too   For this in Visual Studio put a breakpoint on code in question and when debugger hits it rigth click and find  Go To Assembly    or press CTRL ALT D   Second approach is to generate assembly listings while compiling  For this go to project settings -   C C   -  Output Files -  ASM List Location and fill in file name  Also select  Assembly Output  to  Assembly With Source Code   Compile the program and use any third-party debugger  You can use OllyDbg or WinDbg for this  Also you can use IDA  interactive disassembler   But this is hardcore way of doing it

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The earlier version of this answer  a  hack  for rextester com  is mostly redundant now that http   gcc godbolt org  provides CL 19 RC for ARM  x86  and x86-64  targeting the Windows calling convention  unlike gcc  clang  and icc on that site    The Godbolt compiler explorer is designed for nicely formatting compiler asm output  removing the  noise  of directives  so I d highly recommend using it to look at asm for simple functions that take args and return a value  so they won t be optimized away    For a while  CL was available on http   gcc beta godbolt org  but not the main site  but now it s on both     To get MSVC asm output from the http   rextester com l cpp online compiler visual online compiler  Add  FAs to the command line options   Have your program find its own path and work out the path to the  asm and dump it   Or run a disassembler on the  exe   e g  http   rextester com OKI40941   include  lt string gt   include  lt boost filesystem hpp gt   include  lt Windows h gt   using namespace std   static string my exe void       char buf MAX PATH       DWORD tmp   GetModuleFileNameA  NULL     self                                   buf  MAX PATH       return buf     int main         string dircmd    dir        boost  filesystem  path p  my exe            boost  filesystem  path dir   p parent path            transform c  foo bar 1234 a exe         into      c  foo bar 1234 1234 asm     p remove filename        system    dircmd   p string    c str           auto subdir   p end            pointing at one-past the end     subdir--                       pointing at the last directory name     p     subdir                   append the last dir name as a filename     p replace extension   asm        system    string  type      p string    c str            std  cout  lt  lt   Hello  world  n          code of functions you want to see the asm for goes here       type is the DOS version of cat   I didn t want to include more code that would make it harder to find the functions I wanted to see the asm for    Although using std  string and boost run counter to those goals   Some C-style string manipulation that makes more assumptions about the string it s processing  and ignores max-length safety   allocation by using a big buffer  on the result of GetModuleFileNameA would be much less total machine code    IDK why  but cout  lt  lt  p string    lt  lt  endl only shows the basename  i e  the filename  without the directories   even though printing its length shows it s not just the bare name    Chromium48 on Ubuntu 15 10    There s probably some backslash-escape processing at some point in cout  or between the program s stdout and the web browser

User · Answer

If you are talking about debugging to see the assembly code  the easiest way is Debug- Windows- Disassembly  or Alt-8   This will let you step into a called function and stay in Disassembly

[visual-c++] How to view the assembly behind the code using Visual C++?

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