#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
…
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.
69) An additional category,placemarkers,is used internally in translation phase 4 (see 6.10.3.3); it cannot
occur in source files.
请注意,此定义下,“或”不是标点符号.
