C++ 检查字符串是否为空格或空
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C++ check if string is space or null
提问by Mark
Basically I have string of whitespace " "or blocks of whitespace or ""empty in some of the lines of the files and I would like to know if there is a function in C++ that checks this.
基本上，我在文件的某些行中有一串空格" "或空格块或""空白，我想知道 C++ 中是否有一个函数来检查这一点。
*note:* As a side question, in C++ if I want to break a string down and check it for a pattern which library should I use? If I want to code it myself which basic functions should I know to manipulate string? Are there any good references?
*注意：* 作为一个附带问题，在 C++ 中，如果我想分解一个字符串并检查它的模式，我应该使用哪个库？如果我想自己编写代码，我应该知道哪些基本函数来操作字符串？有什么好的参考吗？
采纳答案by Ben Voigt
Since you haven't specified an interpretation of characters > 0x7f, I'm assuming ASCII (i.e. no high characters in the string).
由于您没有指定字符的解释 > 0x7f，我假设是 ASCII（即字符串中没有高位字符）。
#include <string>
#include <cctype>
// Returns false if the string contains any non-whitespace characters
// Returns false if the string contains any non-ASCII characters
bool is_only_ascii_whitespace( const std::string& str )
{
auto it = str.begin();
do {
if (it == str.end()) return true;
} while (*it >= 0 && *it <= 0x7f && std::isspace(*(it++)));
// one of these conditions will be optimized away by the compiler,
// which one depends on whether char is signed or not
return false;
}
回答by Jonathan Grynspan
std::string str = ...;
if (str.empty() || str == " ") {
// It's empty or a single space.
}
回答by Tyler Davis
bool isWhitespace(std::string s){
for(int index = 0; index < s.length(); index++){
if(!std::isspace(s[index]))
return false;
}
return true;
}
回答by jonsca
std::string mystr = "hello";
if(mystr == " " || mystr == "")
//do something
In breaking a string down, std::stringstreamcan be helpful.
在打破字符串时，std::stringstream可能会有所帮助。
回答by Cheers and hth. - Alf
You don't have a nullstring "in some of the lines of the files".
“在文件的某些行中”没有空字符串。
But you can have an empty string, i.e. an empty line.
但是你可以有一个空字符串，即一个空行。
You can use e.g. std::string.length, or if you like C better, strlenfunction.
您可以使用 eg std::string.length，或者如果您更喜欢 C，则使用strlen函数。
In order to check for whitespace, the isspacefunction is handy, but note that for charcharacters the argument should be casted to unsigned char, e.g., off the cuff,
为了检查空格，该isspace函数很方便，但请注意，对于char字符，应将参数强制转换为unsigned char，例如，袖口外，
bool isSpace( char c )
{
typedef unsigned char UChar;
return bool( ::isspace( UChar( c ) ) );
}
Cheers & hth.,
干杯 & hth.,
回答by Dani
If you want pattern checking use regexp.
如果您想要模式检查，请使用正则表达式。
