How to find define inpreprocess and assembly
Created on: April 14, 2025
Created on: April 14, 2025
How to find define inpreprocess and assembly
It looks like you're asking how to find #define
directives during preprocessing and in assembly. Here's how to approach this in C/C++ compilation:
When you're interested in seeing how #define
macros are expanded before compilation, you want to look at the preprocessed output.
-E
flag with GCC/Clang:bashgcc -E your_file.c -o your_file.i
#define
s, #include
s, etc.your_file.i
for the expanded macros.c#define PI 3.14 float area = PI * r * r;
After preprocessing:
cfloat area = 3.14 * r * r;
When you compile your code to assembly, all macros are already expanded. However, you can still generate assembly to inspect what happened.
-S
flag with GCC/Clang:bashgcc -S your_file.c -o your_file.s
#define
s are gone (replaced with their values), but you can see the resulting machine instructions.If PI
is used in math, you’ll see the numeric constant in the assembly (e.g., 3.14
), but not the name PI
.
To keep track of where macros were used:
bashgcc -g -E your_file.c -o your_file.i
Or for tracing macro definitions and usage:
bashgcc -dM -E your_file.c
This prints all macros defined (including predefined ones).
Would you like help analyzing a specific macro or code snippet?
Great! From your image, you're working with this C++ code in nano, and you've defined a macro:
cpp#define PI 353581237
Used in this line:
cppmap<int,pair<double,int8_t>> m = {{1, {PI, '1'}}};
You want to see where PI
is used in both:
Here’s how to do it on your Linux terminal:
Run this in your terminal:
bashg++ -E your_file.cpp -o out.i
Then open out.i
in any editor or less
:
bashless out.i
Search for PI
using /PI
, and you’ll see it replaced with 353581237
.
You can also list all macros with:
bashg++ -dM -E your_file.cpp
That will show:
cpp#define PI 353581237
Now compile to assembly:
bashg++ -S your_file.cpp -o out.s
Then open out.s
:
bashless out.s
Look for the number 353581237
— this is the constant that PI
was replaced with during preprocessing, and it might appear in a mov
instruction or constant pool (depending on optimization and how it’s used).
If you want to see both macro expansion and get more debug-friendly output:
bashg++ -E -P your_file.cpp -o out_clean.i
The -P
flag removes #line
directives, making the file cleaner to read.
Would you like me to generate or simulate what the preprocessed or assembly file would look like for your code?
I cant find my define in assembly
If you can’t find your #define PI 353581237
in the assembly, that’s actually expected behavior due to how the C++ preprocessor and compiler work.
Here’s why — and how to trace it:
PI
in Assembly#define PI 353581237
is a macro, and it's replaced by the literal value (353581237
) at preprocessing time..s
file), there is no memory of the name PI
— it's just a numeric literal.353581237
in the .s
file, depending on:
-O0
to disable optimizations:bashg++ -S -O0 your_file.cpp -o out.s
Optimizations might fold constants, inline values, or remove unused code entirely.
grep
to look for the value:bashgrep 353 out.s
This helps you find:
asmmovl $353581237, %eax
Or something similar (in AT&T syntax).
If you're using Intel syntax (with -masm=intel
), it might look like:
asmmov eax, 353581237
To guarantee it ends up in assembly:
cppint a = PI;
Then build:
bashg++ -S -O0 -o out.s your_file.cpp
And search again in out.s
.
bashg++ -E your_file.cpp -o out.i
Then search for PI
or 353581237
:
bashgrep 353 out.i
If you still don’t see it, paste or upload the .s
file and I’ll help analyze where it might be hiding!