How value substitute

I have defined preprocessor directive value in code.

Code:

---

#include<stdio.h>

#define value 1


int main ()
{
    int x;
    x = value; // 1 substitute for the value 
    printf(" x = %d", x);
   
    return 0;
}

---

I don't understand when 1 will subsitute for value. Does it substitute after code compile or it substitute before code compile ?

C Preprocessor Directives - C and C++ Syntax Reference - Cprogramming.com

It happens before.

Code:

---

$ gcc -E foo.c | tail

# 6 "foo.c"
int main ()
{
    int x;
    x = 1;
    printf(" x = %d", x);

    return 0;
}

---

The -E option allows you to see what your code looks like after it's been through the pre-processor.
This is what the compiler proper will compile.

Note that all your #include files are expanded at this time, so the output of -E gets large pretty quickly.

Quote:

---

Originally Posted by stahta01

C Preprocessor Directives - C and C++ Syntax Reference - Cprogramming.com

---

i have read but my misunderstanding are not getting cleared

Quote:

---

Originally Posted by Salem

It happens before.
[code]
$ gcc -E foo.c | tail
The -E option allows you to see what your code looks like after it's been through the pre-processor.
This is what the compiler proper will compile.

Note that all your #include files are expanded at this time, so the output of -E gets large pretty quickly.

---

I tried command gcc -E hello.c | tail

I get following message

'tail' is not recognized as an internal or external command,
operable program or batch file.

I am using windows 10 operating system

Quote:

---

Originally Posted by Dadu@

I tried command gcc -E hello.c | tail

I get following message

'tail' is not recognized as an internal or external command,
operable program or batch file.

I am using windows 10 operating system

---

'tail' is a unix command. I am not sure there is a a windows equivalent but if you can probably get it via cygwin. Maybe via some other ways too?

Poor windows users can probably get by with
gcc -E foo.c > foo.txt
Then load the resulting text file in an editor.

Quote:

---

Originally Posted by Salem

Poor windows users can probably get by with
gcc -E foo.c > foo.txt
Then load the resulting text file in an editor.

---

gcc -E hello.c > hello.txt

one text file generates after running command. I don't know next what I need to do? How it's releated to my original question

Code:

---

# 1 "hello.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "hello.c"


# 2 "hello.c" 2










# 6 "hello.c"
int main ()
{
    int x;
    x = 1;
    printf(" x = %d", x);


    return 0;
}

---

You wanted to see what the pre-processor did.

And this shows you.

Before
Attachment 16450

After
Attachment 16451

Quote:

---

Originally Posted by Salem

You wanted to see what the pre-processor did.

---

I tried different code
hello.c

Code:

---

#include<stdio.h>#define add(y) ((y) + 1)


int main ()
{
        int y = 5;


        printf("y = %d ", add(y));
       
        return 0;
}

---

what should be observed in this text file

hello.text

Code:

---

# 1 "hello.c"# 1 "<built-in>"
# 1 "<command-line>"
# 1 "hello.c"





# 2 "hello.c" 2






# 4 "hello.c"
int main ()
{
 int y = 5;


 printf("y = %d ", ((y) + 1));


 return 0;
}

---

This may help understand some of the broader ideas: Why function implementations shouldn't be put in header files.