#define STR_START " #define STR_END " int puts(const char *); int main() { puts(STR_START hello world STR_END); }
当我使用gcc编译它(注意:与clang类似的错误),它失败,与这些错误:
$gcc test.c test.c:1:19: warning: missing terminating " character test.c:2:17: warning: missing terminating " character test.c: In function ‘main’: test.c:7: error: missing terminating " character test.c:7: error: ‘hello’ undeclared (first use in this function) test.c:7: error: (Each undeclared identifier is reported only once test.c:7: error: for each function it appears in.) test.c:7: error: expected ‘)’ before ‘world’ test.c:7: error: missing terminating " character
有什么困惑我,所以我通过预处理器运行:
$gcc -E test.c # 1 "test.c" # 1 "" # 1 "" # 1 "test.c" test.c:1:19: warning: missing terminating " character test.c:2:17: warning: missing terminating " character int puts(const char *); int main() { puts(" hello world "); }
如果,C中的宏只是一个文本替换,为什么我的初始例子会失败?这是编译器的错误吗?如果没有,在标准中哪里有与这种情况有关的信息?
注意:我不是在寻找如何使我的初始代码段编译.我只是想了解为什么这种情况失败的信息.
解决方法
6.4 Lexical elements
69) An additional category,placemarkers,is used internally in translation phase 4 (see 6.10.3.3); it cannot
…
3 A token is the minimal lexical element of the language in translation phases 7 and 8. The
categories of tokens are: keywords,identifiers,constants,string literals,and punctuators.
A preprocessing token is the minimal lexical element of the language in translation
phases 3 through 6. The categories of preprocessing tokens are: header names,
identifiers,preprocessing numbers,character constants,punctuators,and
single non-white-space characters that do not lexically match the other preprocessing
token categories.69) If a'
or a"
character matches the last category,the behavior is
undefined. Preprocessing tokens can be separated by white space; this consists of
comments (described later),or white-space characters (space,horizontal tab,new-line,
vertical tab,and form-Feed),or both. As described in 6.10,in certain circumstances
during translation phase 4,white space (or the absence thereof) serves as more than
preprocessing token separation. White space may appear within a preprocessing token
only as part of a header name or between the quotation characters in a character constant
or string literal.
occur in source files.
请注意,此定义下,“或”不是标点符号.
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