vs编译工作正常, g++编译报错

[dragon-dan]

use spdlog header-only
vs2022 ok，g++ 9.3.0 build error

spdlog-1.14.0/include/spdlog/spdlog.h:296:98: error: expected primary-expression before )' token
296 | (logger)->log(spdlog::source_loc{FILE, LINE, SPDLOG_FUNCTION}, level, VA_ARGS)
| ^

need help

ps：
SPDLOG_LOGGER_INFO(logger, "hello"); ==> SPDLOG_LOGGER_INFO(logger, "hello", 0);
then g++ ok

[tt4g]

Can you write problems in English?
Issues in this repository use English.

[dragon-dan]

Can you write problems in English? Issues in this repository use English.

As you wish

[tt4g]

ps：
SPDLOG_LOGGER_INFO(logger, "hello"); ==> SPDLOG_LOGGER_INFO(logger, "hello", 0);
then g++ ok

The compiler prints the macro as the cause of the error, but I don't know if the code is really the cause.
Also, it doesn't make sense that adding an argument to the macro would resolve error expected primary-expression before )' token.

Can you provide the code from your project where the problem occurred (the minimal code that can reproduce the problem)?

[dragon-dan]

#define s_info(fmt, ...) \
    SPDLOG_LOGGER_INFO(multi_logger, fmt, __VA_ARGS__);

use once in the code after initialization
s_info("hello");

windows build run ok, linux build error, I don't know if it's a compiler issue

[tt4g]

This is a well-known problem that occurs when using __VA_ARGS__.
If none of the arguments corresponding to __VA_ARGS__ are passed when the macro is expanded, __VA_ARGS__ will expand to "nothing".
However, the "," before __VA_ARGS__ will remain, resulting in a syntax error.

In other words, your macro is resolved as follows:

// Before
s_info("hello");

// After
SPDLOG_LOGGER_INFO(multi_logger, fmt, );;

, ) is the cause of expected primary-expression before )' token reported by GCC.

There are workarounds, such as __VA_OPT__ added in C++20.
See the following URL for more information.

• c++ - Variadic macros with zero arguments - Stack Overflow
• c - Variadic Macro Expansion: Expected primary expression before ) when VA_ARGS is used - Stack Overflow