## symbol in C language

Dear all,
I am reading existing source code, and meet ## symbol

Really I don't know what does this symbol mean?

The line of code is:

Code:

char *cli_name ## _help[] = {##ARGS, NULL};

Can you show me the meaning of ## ?

Read up on the C preprocessor, in particular on token concatenation.

Dear laserlight

I only found this section:

Code:

${variable##prefix}
Substitute the value of variable, but first discard from that variable any portion at the beginning that matches the pattern prefix. 

If there is more than one alternative for how to match against prefix, this construct uses the longest possible match. 

Thus, ‘${foo##*t}’ substitutes ‘or’, because the largest match for ‘*t’ at the beginning of ‘tractor’ is ‘tract’.

from: The GNU C Library

But, actually, I don't understand its meaning

You should be reading about the language feature of the preprocessor, not on the library.

Can you give me a link

Dear laserlight

I found it, ## is used to concatenate two strings

Preprocessor directives - C++ Documentation

Thank you very much for your help

Originally Posted by Hannibal2010

I found it, ## is used to concatenate two strings

Actually, it concatenates two tokens.

The term string has a particular meaning in C, and ## does not concatenate them.

Originally Posted by Hannibal2010

The line of code is:

Code:

char *cli_name ## _help[] = {##ARGS, NULL};

I check ansi c 99 standard, the ## symbol only available in the replacement list for the macro definition, and it shall not occur at the beginning or at the end of a replacement list. Can you paste the whole document nor even share your reading project to me?