问题
I have a std::vector<std::string> temp_results
and I wish to use std::for_each to go through this vector and concatenate a string, so I concocted the following construction:
std::stringstream ss;
std::string res = std::for_each(temp_results.begin(), temp_results.end(), boost::bind(addup, _1, ss));
std::string addup(std::string str, std::stringstream ss)
{
ss << str;
ss << ";";
return ss.str;
}
I get the following error, which is beyond my understanding:
error C2475: 'std::basic_stringstream<_Elem,_Traits,_Alloc>::str' : forming a pointer-to-member requires explicit use of the address-of operator ('&') and a qualified name
with
[
_Elem=char,
_Traits=std::char_traits<char>,
_Alloc=std::allocator<char>
]
Could someone please explain what is wrong?
回答1:
If, by writing return ss.str;
you intend to call the str
member function from std::stringstream
, then you are missing a pair of parenthesis :
return ss.str();
Also, your code probably won't do what you expect. If you want every call to addup
to work on the same std::stringstream
instance, you have to take it by reference : modify the addup
signature and add a boost::ref()
around the ss
parameter in the boost::bind
.
Here is a working version which I presume does what you expect :
void addup(std::string str, std::stringstream &ss)
{
ss << str;
ss << ";";
}
int main()
{
std::vector<std::string> temp_results;
/* ... */
std::stringstream ss;
std::for_each(temp_results.begin(), temp_results.end(), boost::bind(addup, _1, boost::ref(ss)));
std::cout << ss.str() << std::endl;
}
An alternative using boost::lambda
:
std::for_each(temp_results.begin(), temp_results.end(), ss << boost::lambda::_1 << ';');
来源:https://stackoverflow.com/questions/4447980/stdstringstream-as-parameter-to-a-function