Concatenate string literal with char literal - c

Question

I want to concat a string literal and char literal. Being syntactically incorrect, "abc" 'd' "efg" renders a compiler error:
x.c:4:24: error: expected ',' or ';' before 'd'
By now I have to use snprift (needlessly), despite the value of string literal and the char literal being know at compile time.
I tried
#define CONCAT(S,C) ({ \
static const char *_r = { (S), (C) }; \
_r; \
})
but it does not work because the null terminator of S is not stripped. (Besides of giving compiler warnings.)
Is there a way to write a macro to use
"abc" MACRO('d') "efg" or
MACRO1(MACRO2("abc", 'd'), "efg") or
MACRO("abc", 'd', "efg") ?
In case someone asks why I want that: The char literal comes from a library and I need to print the string out as a status message.

Answer 1

If you can live with the single quotes being included with it, you could use stringification:
#define SOME_DEF 'x'
#define STR1(z) #z
#define STR(z) STR1(z)
#define JOIN(a,b,c) a STR(b) c
int main(void)
{
const char *msg = JOIN("Something to do with ", SOME_DEF, "...");
puts(msg);
return 0;
}
Depending on the context that may or may not be appropriate, but as far as convincing it to actually be a string literal buitl this way, it's the only way that comes to mind without formatting at runtime.

Answer 2

Try this. It uses the C macro trick of double macros so the macro argument has the chance to expand before it is stringified.
#include <stdio.h>
#define C d
#define S "This is a string that contains the character "
#define STR(s) #s
#define XSTR(s) STR(s)
const char* str = S XSTR(C);
int main()
{
puts(str);
return 0;
}

Answer 3

I came up with a GCC-specific solution that I don't like too much, as one cannot use CONCAT nestedly.
#include <stdio.h>
#define CONCAT(S1,C,S2) ({ \
static const struct __attribute__((packed)) { \
char s1[sizeof(S1) - 1]; \
char c; \
char s2[sizeof(S2)]; \
} _r = { (S1), (C), (S2) }; \
(const char *) &_r; \
})
int main(void) {
puts(CONCAT ("abc", 'd', "efg"));
return 0;
}
http://ideone.com/lzEAn

Answer 4

C will only let you concatenate string literals. Actually, there's nothing wrong with snprintf(). You could also use strcpy():
strcpy(dest, str1);
dest[strlen(dest)] = c;
strcpy(dest + strlen(dest) + 1, str2);
You could also use a giant switch statement to overcome this limitation:
switch(c) {
case 'a':
puts("part1" "a" "part2");
break;
case 'b':
puts("part1" "b" "part2");
break;
/* ... */
case 'z':
puts("part1" "z" "part2");
break;
}
...but I refuse to claim any authorship.
To put it short, just stick with snprintf().