How do you get assembler output from C/C++ source

Question

How does one do this?

If I want to analyze how something is getting compiled, how would I get the emitted assembly code?

Answer 1

Here are the steps to see/print the assembly code of any C program on your Windows

console /terminal/ command prompt :

1. Write a C program in a C code editor like codeblocks and save it with an extention .c

2. Compile and run it.

3. Once run successfully, go to the folder where you have installed your gcc compiler and give the

   following command to get a ' .s ' file of the ' .c' file

   C:\ gcc> gcc -S complete path of the C file ENTER

   An example command ( as in my case)

   C:\gcc> gcc -S D:\Aa_C_Certified\alternate_letters.c

   This outputs a ' .s' file of the original ' .c' file

4 . After this , type the following command

C;\gcc> cpp filename.s ENTER

Example command ( as in my case)

C;\gcc> cpp alternate_letters.s

This will print/output the entire Assembly language code of your C program.

Answer 2

This will generate the asm code with the C code + line numbers interweaved to more easily see what lines generate what code.

# create assembler code:
c++ -S -fverbose-asm -g -O2 test.cc -o test.s
# create asm interlaced with source lines:
as -alhnd test.s > test.lst

Found in Algorithms for programmers, page 3 (which is the overall 15th page of the PDF).

Answer 3

Use the -S switch

g++ -S main.cpp

or also with gcc

gcc -S main.c

Also see this

Answer 4

Use the -S option:

gcc -S program.c

Answer 5

If you're looking for LLVM assembly:

llvm-gcc -emit-llvm -S hello.c

Answer 6

I don't see this possibility among answers, probably because the question is from 2008, but in 2018 you can use Matt Goldbolt's online website https://godbolt.org

You can also locally git clone and run his project https://github.com/mattgodbolt/compiler-explorer