#include <iostream>

#define date 2019'07L

#define S(x) #x

int main()
{
  std::cout << S(date) << std::endl;
}

<source>:3:18: error: pasting &quot;x&quot; and &quot;2019'07L&quot; does not give a valid preprocessing token
    3 | #define S(y) cat(x, y)
      |                  ^
<source>:2:19: note: in definition of macro 'cat'
    2 | #define cat(x, y) x ## y
      |                   ^
<source>:4:18: note: in expansion of macro 'S'
    4 | const char s[] = S(date);
      |                  ^
<source>:3:18: error: 'x' was not declared in this scope
    3 | #define S(y) cat(x, y)
      |                  ^
<source>:2:19: note: in definition of macro 'cat'
    2 | #define cat(x, y) x ## y
      |                   ^
<source>:4:18: note: in expansion of macro 'S'
    4 | const char s[] = S(date);
      |                  ^

<source>:4:18: error: pasting formed 'x2019'07L', an invalid preprocessing token
const char s[] = S(date);
                 ^
<source>:3:14: note: expanded from macro 'S'
#define S(y) cat(x, y)
             ^
<source>:2:21: note: expanded from macro 'cat'
#define cat(x, y) x ## y
                    ^
<source>:4:18: error: use of undeclared identifier 'x'
<source>:3:14: note: expanded from macro 'S'
#define S(y) cat(x, y)
             ^
<source>:2:19: note: expanded from macro 'cat'
#define cat(x, y) x ## y
                  ^
<source>:3:18: note: expanded from macro 'x'
#define S(y) cat(x, y)
                 ^
<source>:4:20: error: expected ';' after top level declarator
const char s[] = S(date);
                   ^
<source>:1:14: note: expanded from macro 'date'
#define date 2019'07L
             ^
3 errors generated.

example.cpp
<source>(4): error C2001: newline in constant
<source>(4): error C2065: 'x2019': undeclared identifier
<source>(4): error C2143: syntax error: missing ';' before 'constant'
<source>(4): error C2059: syntax error: 'constant'

#define date 201907L
#define cat(x, y) x ## y
#define S(y) cat(x, y)

const char s[] = S(date);

x.cc:6:18: error: ‘x201907L’ was not declared in this scope
    6 | #define S(y) cat(x, y)