I have a string like this:
aaa bbb
There is a space before the 2nd part of the string.
My goal is to parse only the first part, so aaa.
Everything after the space is out.
How can I do this in C++?
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1possible duplicate of How do I tokenize a string in C++?Karl Knechtel– Karl Knechtel2011-11-24 11:07:34 +00:00Commented Nov 24, 2011 at 11:07
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1@KarlKnechtel: wrong dup / do not close He wants the first part, not all. General tokeniziation is an unnecessary performance waste here.Sebastian Mach– Sebastian Mach2011-11-24 11:21:31 +00:00Commented Nov 24, 2011 at 11:21
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@phresnel I agree, but while this seems like exactly the sort of thing that's constantly asked, I couldn't find a better duplicate.Karl Knechtel– Karl Knechtel2011-11-24 11:22:34 +00:00Commented Nov 24, 2011 at 11:22
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1@KarlKnechtel: If you couldn't, then it isn't, imho.Sebastian Mach– Sebastian Mach2011-11-24 11:23:48 +00:00Commented Nov 24, 2011 at 11:23
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4 Answers
std::string s = "aaa bbb";
std::string s_before_space = s.substr(0, s.find(' '));
1 Comment
user1056635
This is the best solution. Smart, fast, clear and very useful. Thank you!
std::string s = "aaa bbb";
s = s.substr(0, s.find_first_of(' '));
Comments
std::string s = "aaa bbb";
std::istringstream ss(s);
std::string token;
if (ss>>token) // or: while(ss>>token) for _all_ tokens
{
std::cout << "first token only: " << token << std::endl;
}
Alternatively, with a container and using <algorithm>
std::string s = "aaa bbb";
std::istringstream ss(s);
std::vector<std::string> elements;
std::copy(std::istream_iterator<std::string>(ss),
std::istream_iterator<std::string>(),
std::back_inserter(elements));
// elements now contains the whitespace delimited tokens
Includes:
#include <sstream> // for ostringstream/istringstream/stringstream
#include <algorithm> // for copy
#include <iterator> // for istream_iterator/back_inserter
5 Comments
Sebastian Mach
But he only wants the first part, not all. General tokenization here = waste of performance.
jrok
I tried the second method of yours; the vector is empty after
std::copy call.
sehe
@phresnel: then just make it
if (ss>>token) { ... }? I'd prefer str.substr(0, str.find_first_of(" \t"))` thoughSebastian Mach
@sehe: Like the first part better now :)
sehe
@jrok: oops, blatant typo - fixed now. Thanks for reporting!
user following tokenizer, taken from some earlier post on this site.
void Tokenize(const std::string& str, std::vector<std::string>& tokens,const std::string& delimiters = " ") {
std::string::size_type lastPos = str.find_first_not_of(delimiters, 0);
std::string::size_type pos = str.find_first_of(delimiters, lastPos);
while (std::string::npos != pos || std::string::npos != lastPos){
tokens.push_back(str.substr(lastPos, pos - lastPos));
lastPos = str.find_first_not_of(delimiters, pos);
pos = str.find_first_of(delimiters, lastPos);
}
}
1 Comment
Sebastian Mach
But he only wants the first part, not all. General tokenization here = waste of performance. -1 because you just pasted without explanation.