c - c99 内联语义与 gcc (mspgcc)

Question

我正在编写几个我想内联的函数。

阅读此处并在所有声明和定义中使用带有 inline 的第二个 c99 内联选项，如下所示：

extern inline void SPFD54124B_write_cmd(uint16_t command);

在标题中，并且

inline void SPFD54124B_write_cmd(uint16_t command)
{
    spi_write(command, CMD_WIDTH);
}

在相应的 c 文件中。我期待获得函数的内联版本。

但是当我编译时，我得到：

Generating dependencies dep/spi.d from src/spi.c
Generating dependencies dep/spfd54124b.d from src/spfd54124b.c
Generating dependencies dep/pomodoro.d from src/pomodoro.c
Generating dependencies dep/font8x8_ualnum.d from src/font8x8_ualnum.c
Generating dependencies dep/font8x8_basic.d from src/font8x8_basic.c
Generating dependencies dep/evading_util.d from src/evading_util.c
Compiling src/evading_util.c
Compiling src/font8x8_basic.c
Compiling src/font8x8_ualnum.c
Compiling src/pomodoro.c
src/spfd54124b.h:96:20: warning: inline function 'SPFD54124B_write_pixel' declared but never defined [enabled by default]
src/spfd54124b.h:95:20: warning: inline function 'SPFD54124B_write_param' declared but never defined [enabled by default]
src/spfd54124b.h:94:20: warning: inline function 'SPFD54124B_write_cmd' declared but never defined [enabled by default]
src/spi.h:22:20: warning: inline function 'spi_write' declared but never defined [enabled by default]
src/spfd54124b.h:96:20: warning: inline function 'SPFD54124B_write_pixel' declared but never defined [enabled by default]
src/spfd54124b.h:95:20: warning: inline function 'SPFD54124B_write_param' declared but never defined [enabled by default]
src/spfd54124b.h:94:20: warning: inline function 'SPFD54124B_write_cmd' declared but never defined [enabled by default]
src/spi.h:22:20: warning: inline function 'spi_write' declared but never defined [enabled by default]
src/pomodoro.c: In function 'main':
src/spfd54124b.h:94:20: warning: inlining failed in call to 'SPFD54124B_write_cmd': function body not available [-Winline]
src/pomodoro.c:29:25: warning: called from here [-Winline]
src/spfd54124b.h:94:20: warning: inlining failed in call to 'SPFD54124B_write_cmd': function body not available [-Winline]
src/pomodoro.c:31:25: warning: called from here [-Winline]
src/spfd54124b.h:94:20: warning: inlining failed in call to 'SPFD54124B_write_cmd': function body not available [-Winline]
src/pomodoro.c:35:25: warning: called from here [-Winline]
src/spfd54124b.h:94:20: warning: inlining failed in call to 'SPFD54124B_write_cmd': function body not available [-Winline]
src/pomodoro.c:36:25: warning: called from here [-Winline]
src/spfd54124b.h:96:20: warning: inlining failed in call to 'SPFD54124B_write_pixel': function body not available [-Winline]
src/pomodoro.c:40:31: warning: called from here [-Winline]
src/spfd54124b.h:94:20: warning: inlining failed in call to 'SPFD54124B_write_cmd': function body not available [-Winline]
src/pomodoro.c:43:25: warning: called from here [-Winline]
Compiling src/spfd54124b.c
src/spi.h:22:20: warning: inline function 'spi_write' declared but never defined [enabled by default]
src/spi.h:22:20: warning: inline function 'spi_write' declared but never defined [enabled by default]
src/spfd54124b.c: In function 'SPFD54124B_init':
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:124:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:124:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spfd54124b.c: In function 'SPFD54124B_read':
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:25:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:29:14: warning: called from here [-Winline]
src/spfd54124b.c: In function 'SPFD54124B_write_cmd':
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:124:14: warning: called from here [-Winline]
src/spfd54124b.c: In function 'SPFD54124B_write_param':
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spfd54124b.c: In function 'SPFD54124B_write_pixel':
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spfd54124b.c: In function 'SPFD54124B_setrow':
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:124:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spfd54124b.c: In function 'SPFD54124B_setcol':
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:124:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spfd54124b.c: In function 'SPFD54124B_lputch':
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:124:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spfd54124b.c: In function 'SPFD54124B_putch':
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:124:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
src/spi.h:22:20: warning: inlining failed in call to 'spi_write': function body not available [-Winline]
src/spfd54124b.c:129:14: warning: called from here [-Winline]
Compiling src/spi.c
Linking bin/pomodoro.elf

>>>> Size of Firmware <<<<
   text    data     bss     dec     hex filename
   3150       0       2    3152     c50 bin/pomodoro.elf

src/spfd54124b.h:96:20: warning: inline function 'SPFD54124B_write_pixel' declared but never defined [enabled by default]
src/spfd54124b.h:95:20: warning: inline function 'SPFD54124B_write_param' declared but never defined [enabled by default]
src/spfd54124b.h:94:20: warning: inline function 'SPFD54124B_write_cmd' declared but never defined [enabled by default]
src/spi.h:22:20: warning: inline function 'spi_write' declared but never defined [enabled by default]
src/spfd54124b.h:96:20: warning: inline function 'SPFD54124B_write_pixel' declared but never defined [enabled by default]
src/spfd54124b.h:95:20: warning: inline function 'SPFD54124B_write_param' declared but never defined [enabled by default]
src/spfd54124b.h:94:20: warning: inline function 'SPFD54124B_write_cmd' declared but never defined [enabled by default]
src/spi.h:22:20: warning: inline function 'spi_write' declared but never defined [enabled by default]
src/pomodoro.c: In function 'main':
src/spfd54124b.h:94:20: warning: inlining failed in call to 'SPFD54124B_write_cmd': function body not available [-Winline]
src/pomodoro.c:29:25: warning: called from here [-Winline]
src/spfd54124b.h:94:20: warning: inlining failed in call to 'SPFD54124B_write_cmd': function body not available [-Winline]
src/pomodoro.c:31:25: warning: called from here [-Winline]
src/spfd54124b.h:94:20: warning: inlining failed in call to 'SPFD54124B_write_cmd': function body not available [-Winline]
src/pomodoro.c:35:25: warning: called from here [-Winline]
src/spfd54124b.h:94:20: warning: inlining failed in call to 'SPFD54124B_write_cmd': function body not available [-Winline]
src/pomodoro.c:36:25: warning: called from here [-Winline]
src/spfd54124b.h:96:20: warning: inlining failed in call to 'SPFD54124B_write_pixel': function body not available [-Winline]
src/pomodoro.c:40:31: warning: called from here [-Winline]
src/spfd54124b.h:94:20: warning: inlining failed in call to 'SPFD54124B_write_cmd': function body not available [-Winline]
src/pomodoro.c:43:25: warning: called from here [-Winline]

我不确定我是否理解 c99 中不同的内联替代方案。

score 10 · Accepted Answer

你得到的东西与你需要的方式完全不同。在标题中，您应该使用：

inline void SPFD54124B_write_cmd(uint16_t command)
{
    spi_write(command, CMD_WIDTH);
}

在包含此标题的翻译单元中，这将创建一个具有外部链接的内联函数。您还应该在这些翻译单元之一中放置声明：

extern void SPFD54124B_write_cmd(uint16_t);

这（连同inline标题中的定义）将创建函数的外部定义。包含标题但不包含extern声明的其他文件将创建函数的内联定义：该定义仅在该翻译单元中可用，但不禁止在其他地方进行外部定义。

总的来说，您将拥有一个函数的外部定义，并且每个包含头文件的文件也将有一个可用的非外部定义；编译器可以使用任何一个。从概念上讲，在完整的程序中仍然只调用一个函数SPFD54124B_write_cmd——例如，如果你在多个翻译单元中获取函数的地址，你应该得到相同的值。

作为替代方案，您可以将其放在标题中：

static inline void SPFD54124B_write_cmd(uint16_t command)
{
    spi_write(command, CMD_WIDTH);
}

并且根本不使用任何extern声明；这将在每个包含标题的文件中创建一个具有内部链接的内联函数。根本没有函数的外部定义，从概念上讲，每个包含标题的翻译单元都有自己独立的函数副本。

（后人需要注意的是，GCC当前的默认模式是“gnu89”，它没有实现C99语义inline）

score 4 · Accepted Answer

为了确保一个函数 ACTUALLY 可以被内联，它几乎必须在头文件中定义。

如果您不这样做，大多数编译器实际上不会内联该函数。

所以我的建议是将实际函数内容移动到头文件中：

inline void SPFD54124B_write_cmd(uint16_t command)
{
    spi_write(command, CMD_WIDTH);
}

c - c99 内联语义与 gcc (mspgcc)

2 回答 2

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