prc
宏的参数什么情况下会被当作宏定义展开？
[table=95%][tr][td][font=FixedSys][color=#000000][color=#0000CC]#[/color][color=#FF0000]include[/color] [color=#0000CC]<[/color]stdio[color=#0000CC].[/color]h[color=#0000CC]>[/color]
[color=#0000CC]#[/color][color=#FF0000]include[/color] [color=#0000CC]<[/color]stdlib[color=#0000CC].[/color]h[color=#0000CC]>[/color]
[color=#0000CC]#[/color][color=#FF0000]define[/color] STR[color=#0000CC]([/color]x[color=#0000CC])[/color] [color=#0000CC]#[/color]x
[color=#0000CC]#[/color][color=#FF0000]define[/color] YEAR 2008
[color=#0000CC]#[/color][color=#FF0000]define[/color] MONTH 2
[color=#0000CC]#[/color][color=#FF0000]define[/color] DAY 19
[color=#0000CC]#[/color][color=#0000FF]if[/color] 0
[color=#0000CC]#[/color][color=#FF0000]define[/color] TODAY STR[color=#0000CC]([/color]YEAR[color=#0000CC])[/color][color=#FF00FF]"/"[/color]STR[color=#0000CC]([/color]MONTH[color=#0000CC])[/color][color=#FF00FF]"/"[/color]STR[color=#0000CC]([/color]DAY[color=#0000CC])[/color]
[color=#0000CC]#[/color][color=#0000FF]else[/color]
[color=#0000CC]#[/color][color=#FF0000]define[/color] _TODAY[color=#0000CC]([/color]y[color=#0000CC],[/color]m[color=#0000CC],[/color]d[color=#0000CC])[/color] STR[color=#0000CC]([/color]y[color=#0000CC])[/color][color=#FF00FF]"/"[/color]STR[color=#0000CC]([/color]m[color=#0000CC])[/color][color=#FF00FF]"/"[/color]STR[color=#0000CC]([/color]d[color=#0000CC])[/color]
[color=#0000CC]#[/color][color=#FF0000]define[/color] TODAY _TODAY[color=#0000CC]([/color]YEAR[color=#0000CC],[/color]MONTH[color=#0000CC],[/color]DAY[color=#0000CC])[/color]
[color=#0000CC]#[/color][color=#FF0000]endif[/color]
[color=#0000FF]int[/color] main[color=#0000CC]([/color][color=#0000CC])[/color]
[color=#0000CC]{[/color]
[color=#FF0000]printf[/color][color=#0000CC]([/color][color=#FF00FF]"%s"[/color][color=#0000CC],[/color] TODAY[color=#0000CC])[/color][color=#0000CC];[/color]
[color=#0000FF]return[/color] 0[color=#0000CC];[/color]
[color=#0000CC]}[/color][/color][/font][/td][/tr][/table]
采用第一种定义，TODAY被展开成 YEAR/MONTH/DAY
采用第一种定义，TODAY被展开成 2008/2/9
为什么在第二种定义方式中，YEAR MONTH DAY被展开成数字形式；而在第一种定义方式中，YEAR MONTH DAY不会被展开
C语言的标准是怎么定义的？
lenovo
在第二种情况，
TODAY换成_TODAY(YEAR,MONTH,DAY)，
继而换成_TODAY(2008,2,19)。
prc
那为何第一种情况不会
[code]TODAY --> STR(YEAR)"/"STR(MONTH)"/"STR(DAY) --> STR(2008) "/" STR(2) "/" STR(9)[/code]
[[i] 本帖最后由 prc 于 2008-2-19 17:15 编辑 [/i]]
flw2
应该是由于#的特殊性
如果有书翻翻K&R后面，看看有没有讲到，首先要处理这种，我记不清楚了
flw2
找到一个了，#比较特殊
6.10.3.1 Argument substitution
1 After the arguments for the invocation of a function-like macro have been identified,
argument substitution takes place. A parameter in the replacement list, unless preceded
by a # or ## preprocessing token or followed by a ## preprocessing token (see below), is
replaced by the corresponding argument after all macros contained therein have been
expanded. Before being substituted, each argument’s preprocessing tokens are
completely macro replaced as if they formed the rest of the preprocessing file; no other
preprocessing tokens are available.