c - 如何使用宏连接两个正整数？

Question

我需要编写一个程序，使用宏将两个正整数连接起来形成另一个正整数。例如，如果 x=12，y=35，答案应该是 1235。我应该怎么做？

Answer 1

你只需要使用##操作符

It is often useful to merge two tokens into one while expanding macros. This is called token pasting or token concatenation. The ‘##’ preprocessing operator performs token pasting. When a macro is expanded, the two tokens on either side of each ‘##’ operator are combined into a single token, which then replaces the ‘##’ and the two original tokens in the macro expansion. Usually both will be identifiers, or one will be an identifier and the other a preprocessing number. When pasted, they make a longer identifier. This isn’t the only valid case. It is also possible to concatenate two numbers (or a number and a name, such as 1.5 and e3) into a number. Also, multi-character operators such as += can be formed by token pasting.

来自 https://gcc.gnu.org/onlinedocs/cpp/Concatenation.html

因此，在您的情况下，#define CONCAT_NUMBER(FIRST, SECOND) (FIRST ## SECOND) 应该有效