posted Dec 27, 2011, 10:40 AM by Teng-Yok Lee
[
updated Jan 2, 2021, 8:32 PM
]
A short example to use the ## operator for token concatenation (From GCC online documentation):
In http://gcc.gnu.org/onlinedocs/cpp/Concatenation.html#Concatenation: Consider a C program that interprets named commands. There probably
needs to be a table of commands, perhaps an array of structures declared
as follows:
struct command
{
char *name;
void (*function) (void);
};
struct command commands[] =
{
{ "quit", quit_command },
{ "help", help_command },
...
};
It would be cleaner not to have to give each command name twice, once in
the string constant and once in the function name. A macro which takes the
name of a command as an argument can make this unnecessary. The string
constant can be created with stringification, and the function name by
concatenating the argument with `_command'. Here is how it is done:
#define COMMAND(NAME) { #NAME, NAME ## _command }
struct command commands[] =
{
COMMAND (quit),
COMMAND (help),
...
};
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