The obvious approach is to create a simple manipulator and use that. For example, a manipulator using a statically provided char
to determine if the next non-whitespace character is that character and, if so, extracts it could look like this:
#include <iostream>
#include <sstream>
template <char C>
std::istream& expect(std::istream& in)
{
if ((in >> std::ws).peek() == C) {
in.ignore();
}
else {
in.setstate(std::ios_base::failbit);
}
return in;
}
You can then use the thus build manipulator to extract characters:
int main(int ac, char *av[])
{
std::string s(ac == 1? "[ 0.562 , 1.4e-2 ]": av[1]);
float f1 = 0.0f, f2 = 0.0f;
std::istringstream in(s);
if (in >> expect<'['> >> f1 >> expect<','> >> f2 >> expect<']'>) {
std::cout << "read f1=" << f1 << " f2=" << f2 << '\n';
}
else {
std::cout << "ERROR: failed to read '" << s << "'\n";
}
}