如何拥有“弦线”？在与“getline(in,line)”相同的范围内一会儿（getline（...））”环形？
示例：
std::ifstream in("some_file.txt");
std::string line; // must be outside ?
while(getline(in,line)){
// how to make 'line' only available inside of 'while' ?
}
Do-while 循环在第一次迭代中不起作用：
std::ifstream in("some_fule.txt");
do{
std::string line;
// line will be empty on first iteration
}while(getline(in,line));
当然，总是可以有一个 if(line.empty()) getline(...) 但这并不真的感觉正确的。 我还想过滥用逗号运算符：
while(string line, getline(in,line)){
}
但这行不通，MSVC 告诉我这是因为 line 无法转换为 bool。通常，以下序列
statement-1, statement-2, statement-3
应为 type-of statements-3 类型（不考虑重载的operator,）。我不明白为什么那个不起作用。有什么想法吗？
Example:
std::ifstream in("some_file.txt");
std::string line; // must be outside ?
while(getline(in,line)){
// how to make 'line' only available inside of 'while' ?
}
Do-while loops won't work for the first iteration:
std::ifstream in("some_fule.txt");
do{
std::string line;
// line will be empty on first iteration
}while(getline(in,line));
Of course one can always have a if(line.empty()) getline(...) but that doesn't really feel right.
I also thought of abusing the comma operator:
while(string line, getline(in,line)){
}
but that won't work, and MSVC tells me that's because line isn't convertible to bool. Normally, the following sequence
statement-1, statement-2, statement-3
should be of type type-of statement-3 (not taking overloaded operator, into account). I don't understand why that one doesn't work. Any ideas?
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评论（3）
您可以作一点欺骗，只创建一个多余的块：
从技术上讲，这不是“相同的范围”，但只要外部块中没有其他内容，它就是等效的。
You could cheat a little bit and just make a superfluous block:
This isn't technically "the same scope", but as long as there's nothing else in the outer block, it's equivalent.
for 循环就可以了，我一直这样做：
A for loop will work, I do this all the time:
您可以使用
for循环：不过，我认为这不是很好的风格。
You could use a
forloop:I don't think this is very good style, though.