Why parsing empty text in parse_value ?

[mwestphal]

in template <typename T> void parse_value(const std::string& text, std::vector<T>& value) there is a branch for empty text like this:

      if (text.empty()) {
        T v;
        parse_value(text, v);
        value.emplace_back(std::move(v));
        return;
      }    

Why would we ever want to parse empty text ? Why even emplacing back a value in the vector with an empty text ?

This seems to fails and throw in certain cases.

[jarro2783]

This allows an empty string when an option can have multiple values. Otherwise the code after it tries to split text by some delimiter which fails when it is empty.

[mwestphal]

But shouldn't an empty string results in an empty vector? Also with T=double, parse_value throw an exception.

[jarro2783]

No, values are added into a vector. So --value "" adds an empty string to the values for --value.

[mwestphal]

but with T=double, how do you convert the empty string ? to a zero ?

[jarro2783]

well then that's probably invalid input. Do you have an example that shows this doing the wrong thing?

[mwestphal]

It is a bit involved inside a bigger application, I need to take it out in a simple example.

[jarro2783]

If you can just give the expected options and some input that fails that should be enough.

[mwestphal]

Are the callstack of the sigabrt:

Thread 1 "f3d" received signal SIGABRT, Aborted.
0x00007ffff78a149c in ?? () from /usr/lib/libc.so.6
(gdb) bt
#0  0x00007ffff78a149c in ?? () from /usr/lib/libc.so.6
#1  0x00007ffff7851958 in raise () from /usr/lib/libc.so.6
#2  0x00007ffff783b53d in abort () from /usr/lib/libc.so.6
#3  0x00007ffff7a99833 in __gnu_cxx::__verbose_terminate_handler () at /usr/src/debug/gcc/libstdc++-v3/libsupc++/vterminate.cc:95
#4  0x00007ffff7aa5cfc in __cxxabiv1::__terminate (handler=<optimized out>) at /usr/src/debug/gcc/libstdc++-v3/libsupc++/eh_terminate.cc:48
#5  0x00007ffff7aa5d69 in std::terminate () at /usr/src/debug/gcc/libstdc++-v3/libsupc++/eh_terminate.cc:58
#6  0x00007ffff7aa5fcd in __cxxabiv1::__cxa_throw (obj=<optimized out>, tinfo=0x555555685680 <typeinfo for cxxopts::argument_incorrect_type>, 
    dest=0x55555559d6dc <cxxopts::argument_incorrect_type::~argument_incorrect_type()>) at /usr/src/debug/gcc/libstdc++-v3/libsupc++/eh_throw.cc:98
#7  0x000055555559d778 in cxxopts::throw_or_mimic<cxxopts::argument_incorrect_type> (text="") at /home/glow/dev/f3d/src/application/cxxopts.hpp:540
#8  0x000055555560d400 in cxxopts::values::stringstream_parser<double> (text="", value=@0x7fffffffda38: 4.6355705639563209e-310) at /home/glow/dev/f3d/src/application/cxxopts.hpp:929
#9  0x000055555560cbbb in cxxopts::values::parse_value<double, (void*)0> (text="", value=@0x7fffffffda38: 4.6355705639563209e-310) at /home/glow/dev/f3d/src/application/cxxopts.hpp:975
#10 0x000055555560c9ce in cxxopts::values::parse_value<double> (text="", value=std::vector of length 0, capacity 0) at /home/glow/dev/f3d/src/application/cxxopts.hpp:988

So the call is a simple as cxxopts::values::parse_value<double> (text="", value=std::vector of length 0, capacity 0)

Value is an empty vector of double, and cxxopts gets an empty string to parse into the vector. I expect the vector to stay empty and especially to not throw.

Hth

[jarro2783]

Can you give me a bit further up the stack so that I can see what is calling it? It would help if I knew the command line that it was trying to parse.

[mwestphal]

Here is the full cxxopts stack:

#0  0x00007ffff78a149c in ?? () from /usr/lib/libc.so.6
#1  0x00007ffff7851958 in raise () from /usr/lib/libc.so.6
#2  0x00007ffff783b53d in abort () from /usr/lib/libc.so.6
#3  0x00007ffff7a99833 in __gnu_cxx::__verbose_terminate_handler () at /usr/src/debug/gcc/libstdc++-v3/libsupc++/vterminate.cc:95
#4  0x00007ffff7aa5cfc in __cxxabiv1::__terminate (handler=<optimized out>) at /usr/src/debug/gcc/libstdc++-v3/libsupc++/eh_terminate.cc:48
#5  0x00007ffff7aa5d69 in std::terminate () at /usr/src/debug/gcc/libstdc++-v3/libsupc++/eh_terminate.cc:58
#6  0x00007ffff7aa5fcd in __cxxabiv1::__cxa_throw (obj=<optimized out>, tinfo=0x555555686660 <typeinfo for cxxopts::argument_incorrect_type>, 
    dest=0x55555559e99c <cxxopts::argument_incorrect_type::~argument_incorrect_type()>) at /usr/src/debug/gcc/libstdc++-v3/libsupc++/eh_throw.cc:98
#7  0x000055555559ea38 in cxxopts::throw_or_mimic<cxxopts::argument_incorrect_type> (text="") at /home/glow/dev/f3d/src/application/cxxopts.hpp:540
#8  0x000055555560e6c0 in cxxopts::values::stringstream_parser<double> (text="", value=@0x7fffffffcd28: 4.6355705641934724e-310) at /home/glow/dev/f3d/src/application/cxxopts.hpp:929
#9  0x000055555560de7b in cxxopts::values::parse_value<double, (void*)0> (text="", value=@0x7fffffffcd28: 4.6355705641934724e-310) at /home/glow/dev/f3d/src/application/cxxopts.hpp:975
#10 0x000055555560dc8e in cxxopts::values::parse_value<double> (text="", value=std::vector of length 0, capacity 0) at /home/glow/dev/f3d/src/application/cxxopts.hpp:988
#11 0x000055555560c845 in cxxopts::values::abstract_value<std::vector<double, std::allocator<double> > >::parse (this=0x555556240700) at /home/glow/dev/f3d/src/application/cxxopts.hpp:1089
#12 0x000055555559767f in cxxopts::OptionValue::parse_default (this=0x5555562406c0, details=std::shared_ptr<const cxxopts::OptionDetails> (use count 2, weak count 0) = {...})
    at /home/glow/dev/f3d/src/application/cxxopts.hpp:1353
#13 0x0000555555598a17 in cxxopts::OptionParser::parse_default (this=0x7fffffffd150, details=std::shared_ptr<cxxopts::OptionDetails> (use count 2, weak count 0) = {...})
    at /home/glow/dev/f3d/src/application/cxxopts.hpp:2059
#14 0x0000555555599d08 in cxxopts::OptionParser::parse (this=0x7fffffffd150, argc=1, argv=0x7fffffffd268) at /home/glow/dev/f3d/src/application/cxxopts.hpp:2330
#15 0x00005555555992d8 in cxxopts::Options::parse (this=0x7fffffffd530, argc=1, argv=0x7fffffffd268) at /home/glow/dev/f3d/src/application/cxxopts.hpp:2188
#16 0x000055555558dc31 in ConfigurationOptions::GetOptions (this=0x5555556f57a0, appOptions=..., options=..., inputs=std::vector of length 0, capacity 0, 

[mwestphal]

the command line is basically empty (only the program name), and the option has a default, which is an empty vector.

[jarro2783]

is the option set as vector<double> with a default value of an empty string?

[mwestphal]

Yes, exactly.

[jarro2783]

How is your option set? I tried this, but I couldn't reproduce the problem.

("vector", "A list of doubles", cxxopts::value<std::vector<double>>()->default_value(""))

[mwestphal]

Here is a minimal example, keep in mind I'm not really experienced with cxxopts, just a standard user.

int main(int argc, char** argv)
{ 
  cxxopts::Options cxxOptions("name", "title");

  std::vector<double> testOption;
  auto grp0 = cxxOptions.add_options("group");
  auto val = cxxopts::value<std::vector<double>>(testOption);
  // val = val->default_value("0"); // This line behave as expected, outputs "0.0000"
  val = val->default_value(""); // This line throw an error, expected output "empty"
  grp0("test", "doc", val, "help");
  cxxOptions.parse(argc, argv);

  std::string out = testOption.empty() ? "empty" : std::to_string(testOption[0]);
  std::cout<<out<<std::endl;

  exit(EXIT_SUCCESS);
  }

[jarro2783]

That's the problem, you can't set a default like that. You're effectively telling it to have a default value of a single double that is described by an empty string, which doesn't parse as a double.

[mwestphal]

Indeed, this is not about default value specifically but about the parsing of vector option. Reading the doc it seems to be covered by this point here:

Parsing of list of values in form of an std::vector is also supported, as long as T can be parsed

And since "" cant be parsed for double or int, it cant be parsed for std::vector double or std::vector int Of course, std::vector std::string can be parsed but it results not in an empty vector but in a vector of size 1 containing an empty string.

I understand the approach, but I also think that it would be nice to have a way to generate an empty vector using cxxopts.