Concatenate content of string var with string using Macro in C

The preprocessor cannot concatenate the value of a variable with a string it can only concatenate preprocessor tokens that may be the result of a macro expansion.

It would be possible with #define Name OverFlow or similar.

Example file macro.c:

Edit: As suggested by Lundin I added macros to get a string literal in case the variable char *Name = "OverFlow"; is needed for other purposes.

#define NAME OverFlow

#define DEFINE_VAR_2(str) unsigned char u8_##str##_Var
#define DEFINE_VAR(str) DEFINE_VAR_2(str)

/* macros to get a string literal */
#define STR_2(x) #x
#define STR(x) STR_2(x)
#define STRNAME STR(NAME)
#define STRVAR const char *Name = STR(NAME)

/* this works */
DEFINE_VAR(NAME);

/* this doesn't work */
DEFINE_VAR_2(NAME);

/* if you need a string with the variable name */
const char *Name = STRNAME;
/* or with a single macro */
STRVAR;

Result:

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





/* macros to get a string literal as proposed by Lundin */





/* this works */
unsigned char u8_OverFlow_Var;

/* this doesn't work */
unsigned char u8_NAME_Var;

/* if you need a string with the variable name */
const char *Name = "OverFlow";
/* or with a single macro */
const char *Name = "OverFlow";

Ok, here's something that works but may not be what you are looking for exaclty and the gnu documentation link for you to understand C preprocessor

main.c

#include <stdio.h>
#define xstr(s) str(s)
#define str(s) "u8_"#s"_Var"

int main(int argc, char const *argv[])
{
    const char *Overflow;
    printf("name: %s\n", Overflow);
    printf("defined: %s\n", xstr(Overflow));
    return 0;
}

output

name: (null)
defined: u8_Overflow_Var

https://gcc.gnu.org/onlinedocs/cpp/Stringizing.html & https://gcc.gnu.org/onlinedocs/cpp/Concatenation.html#Concatenation

The define works, what are you trying to achieve ?

const char * Name = "OverFlow";
#define DEFINE_VAR(str) unsigned char u8_##str##_Var;
DEFINE_VAR(Name)

int main(int argc, char const *argv[])
{
    printf("%s\n", Name);
    return 0;
}

output result is

OverFlow