C++ debug/print custom type with GDB : the case of nlohmann json library
I'm working on a project using nlohmann's json C++ implementation.
How can one easily explore nlohmann's JSON keys/vals in GDB ?
I tried to use this STL gdb wrapping since it provides helpers to explore STL structures that lohmann's JSON lib is using.
But I don't find it convenient.
Here is a simple use case:
json foo;
foo["flex"] = 0.2;
foo["awesome_str"] = "bleh";
foo["nested"] = {{"bar", "barz"}};
What I would like to have in GDB:
(gdb) p foo
{
"flex" : 0.2,
"awesome_str": "bleh",
"nested": etc.
}
Current behavior
(gdb) p foo
$1 = {
m_type = nlohmann::detail::value_t::object,
m_value = {
object = 0x129ccdd0,
array = 0x129ccdd0,
string = 0x129ccdd0,
boolean = 208,
number_integer = 312266192,
number_unsigned = 312266192,
number_float = 1.5427999782486669e-315
}
}
(gdb) p foo.at("flex")
Cannot evaluate function -- may be inlined // I suppose it depends on my compilation process. But I guess it does not invalidate the question.
(gdb) p *foo.m_value.object
$2 = {
_M_t = {
_M_impl = {
<std::allocator<std::_Rb_tree_node<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long long, unsigned long long, double, std::allocator, nlohmann::adl_serializer> > > >> = {
<__gnu_cxx::new_allocator<std::_Rb_tree_node<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long long, unsigned long long, double, std::allocator, nlohmann::adl_serializer> > > >> = {<No data fields>}, <No data fields>},
<std::_Rb_tree_key_compare<std::less<void> >> = {
_M_key_compare = {<No data fields>}
},
<std::_Rb_tree_header> = {
_M_header = {
_M_color = std::_S_red,
_M_parent = 0x4d72d0,
_M_left = 0x4d7210,
_M_right = 0x4d7270
},
_M_node_count = 5
}, <No data fields>}
}
}
c++ json gdb pretty-print nlohmann-json
add a comment |
I'm working on a project using nlohmann's json C++ implementation.
How can one easily explore nlohmann's JSON keys/vals in GDB ?
I tried to use this STL gdb wrapping since it provides helpers to explore STL structures that lohmann's JSON lib is using.
But I don't find it convenient.
Here is a simple use case:
json foo;
foo["flex"] = 0.2;
foo["awesome_str"] = "bleh";
foo["nested"] = {{"bar", "barz"}};
What I would like to have in GDB:
(gdb) p foo
{
"flex" : 0.2,
"awesome_str": "bleh",
"nested": etc.
}
Current behavior
(gdb) p foo
$1 = {
m_type = nlohmann::detail::value_t::object,
m_value = {
object = 0x129ccdd0,
array = 0x129ccdd0,
string = 0x129ccdd0,
boolean = 208,
number_integer = 312266192,
number_unsigned = 312266192,
number_float = 1.5427999782486669e-315
}
}
(gdb) p foo.at("flex")
Cannot evaluate function -- may be inlined // I suppose it depends on my compilation process. But I guess it does not invalidate the question.
(gdb) p *foo.m_value.object
$2 = {
_M_t = {
_M_impl = {
<std::allocator<std::_Rb_tree_node<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long long, unsigned long long, double, std::allocator, nlohmann::adl_serializer> > > >> = {
<__gnu_cxx::new_allocator<std::_Rb_tree_node<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long long, unsigned long long, double, std::allocator, nlohmann::adl_serializer> > > >> = {<No data fields>}, <No data fields>},
<std::_Rb_tree_key_compare<std::less<void> >> = {
_M_key_compare = {<No data fields>}
},
<std::_Rb_tree_header> = {
_M_header = {
_M_color = std::_S_red,
_M_parent = 0x4d72d0,
_M_left = 0x4d7210,
_M_right = 0x4d7270
},
_M_node_count = 5
}, <No data fields>}
}
}
c++ json gdb pretty-print nlohmann-json
You mean you don't find great joy manually digging through red/black trees to try and find something? ;)
– Retired Ninja
44 mins ago
add a comment |
I'm working on a project using nlohmann's json C++ implementation.
How can one easily explore nlohmann's JSON keys/vals in GDB ?
I tried to use this STL gdb wrapping since it provides helpers to explore STL structures that lohmann's JSON lib is using.
But I don't find it convenient.
Here is a simple use case:
json foo;
foo["flex"] = 0.2;
foo["awesome_str"] = "bleh";
foo["nested"] = {{"bar", "barz"}};
What I would like to have in GDB:
(gdb) p foo
{
"flex" : 0.2,
"awesome_str": "bleh",
"nested": etc.
}
Current behavior
(gdb) p foo
$1 = {
m_type = nlohmann::detail::value_t::object,
m_value = {
object = 0x129ccdd0,
array = 0x129ccdd0,
string = 0x129ccdd0,
boolean = 208,
number_integer = 312266192,
number_unsigned = 312266192,
number_float = 1.5427999782486669e-315
}
}
(gdb) p foo.at("flex")
Cannot evaluate function -- may be inlined // I suppose it depends on my compilation process. But I guess it does not invalidate the question.
(gdb) p *foo.m_value.object
$2 = {
_M_t = {
_M_impl = {
<std::allocator<std::_Rb_tree_node<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long long, unsigned long long, double, std::allocator, nlohmann::adl_serializer> > > >> = {
<__gnu_cxx::new_allocator<std::_Rb_tree_node<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long long, unsigned long long, double, std::allocator, nlohmann::adl_serializer> > > >> = {<No data fields>}, <No data fields>},
<std::_Rb_tree_key_compare<std::less<void> >> = {
_M_key_compare = {<No data fields>}
},
<std::_Rb_tree_header> = {
_M_header = {
_M_color = std::_S_red,
_M_parent = 0x4d72d0,
_M_left = 0x4d7210,
_M_right = 0x4d7270
},
_M_node_count = 5
}, <No data fields>}
}
}
c++ json gdb pretty-print nlohmann-json
I'm working on a project using nlohmann's json C++ implementation.
How can one easily explore nlohmann's JSON keys/vals in GDB ?
I tried to use this STL gdb wrapping since it provides helpers to explore STL structures that lohmann's JSON lib is using.
But I don't find it convenient.
Here is a simple use case:
json foo;
foo["flex"] = 0.2;
foo["awesome_str"] = "bleh";
foo["nested"] = {{"bar", "barz"}};
What I would like to have in GDB:
(gdb) p foo
{
"flex" : 0.2,
"awesome_str": "bleh",
"nested": etc.
}
Current behavior
(gdb) p foo
$1 = {
m_type = nlohmann::detail::value_t::object,
m_value = {
object = 0x129ccdd0,
array = 0x129ccdd0,
string = 0x129ccdd0,
boolean = 208,
number_integer = 312266192,
number_unsigned = 312266192,
number_float = 1.5427999782486669e-315
}
}
(gdb) p foo.at("flex")
Cannot evaluate function -- may be inlined // I suppose it depends on my compilation process. But I guess it does not invalidate the question.
(gdb) p *foo.m_value.object
$2 = {
_M_t = {
_M_impl = {
<std::allocator<std::_Rb_tree_node<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long long, unsigned long long, double, std::allocator, nlohmann::adl_serializer> > > >> = {
<__gnu_cxx::new_allocator<std::_Rb_tree_node<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long long, unsigned long long, double, std::allocator, nlohmann::adl_serializer> > > >> = {<No data fields>}, <No data fields>},
<std::_Rb_tree_key_compare<std::less<void> >> = {
_M_key_compare = {<No data fields>}
},
<std::_Rb_tree_header> = {
_M_header = {
_M_color = std::_S_red,
_M_parent = 0x4d72d0,
_M_left = 0x4d7210,
_M_right = 0x4d7270
},
_M_node_count = 5
}, <No data fields>}
}
}
c++ json gdb pretty-print nlohmann-json
c++ json gdb pretty-print nlohmann-json
edited 1 hour ago
LoneWanderer
asked 7 hours ago
LoneWandererLoneWanderer
1,122825
1,122825
You mean you don't find great joy manually digging through red/black trees to try and find something? ;)
– Retired Ninja
44 mins ago
add a comment |
You mean you don't find great joy manually digging through red/black trees to try and find something? ;)
– Retired Ninja
44 mins ago
You mean you don't find great joy manually digging through red/black trees to try and find something? ;)
– Retired Ninja
44 mins ago
You mean you don't find great joy manually digging through red/black trees to try and find something? ;)
– Retired Ninja
44 mins ago
add a comment |
1 Answer
1
active
oldest
votes
I found my own answer reading further the GDB capabilities and stack overflow questions concerning print of std::string.
Short path
I simply defined a gdb command as follows:
# this is a gdb script
# can be loaded from gdb using
# source my_script.txt (or. gdb or whatever you like)
define pjson
# use the lohmann's builtin dump method, ident 4 and use space separator
printf "%sn", $arg0.dump(4, ' ', true).c_str()
end
# configure command helper (text displayed when typing 'help pjson' in gdb)
document pjson
Prints a lohmann's JSON C++ variable as a human-readable JSON string
end
Using it in gdb:
(gdb) source my_custom_script.gdb
(gdb) pjson foo
{
"flex" : 0.2,
"awesome_str": "bleh",
"nested": {
"bar": "barz"
}
}
Over the top
The other way is to define a GDB pretty printer in python and make it tightly associated to your project (autoloading stuff activated). See this link for an in-depth approach.
Basically, when in gdb you would type:
(gdb) p foo
and GDB will automagically test for foo
's type and invoke the associated pretty printer if any. That would end-up in the same result. The main difference is that it is done using the well-known print
command. The person debugging would not have to learn a new command (like the pjson
defined in the short answer).
Quoting:
A pretty-printer consists of two parts: a lookup function to detect if the type is supported, and the printer itself.
Here is an example showing how a
std::string
printer might be written. See Pretty Printing API, for details on the API this class must provide.
class StdStringPrinter(object):
"Print a std::string"
def __init__(self, val):
self.val = val
def to_string(self):
return self.val['_M_dataplus']['_M_p']
def display_hint(self):
return 'string'
Still quoting for the sake of completness:
And here is an example showing how a lookup function for the printer example above might be written.
def str_lookup_function(val):
lookup_tag = val.type.tag
if lookup_tag == None:
return None
regex = re.compile("^std::basic_string<char,.*>$")
if regex.match(lookup_tag):
return StdStringPrinter(val)
return None
That looks pretty useful. Unfortunately I am out of votes ATM.
– πάντα ῥεῖ
6 hours ago
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
I found my own answer reading further the GDB capabilities and stack overflow questions concerning print of std::string.
Short path
I simply defined a gdb command as follows:
# this is a gdb script
# can be loaded from gdb using
# source my_script.txt (or. gdb or whatever you like)
define pjson
# use the lohmann's builtin dump method, ident 4 and use space separator
printf "%sn", $arg0.dump(4, ' ', true).c_str()
end
# configure command helper (text displayed when typing 'help pjson' in gdb)
document pjson
Prints a lohmann's JSON C++ variable as a human-readable JSON string
end
Using it in gdb:
(gdb) source my_custom_script.gdb
(gdb) pjson foo
{
"flex" : 0.2,
"awesome_str": "bleh",
"nested": {
"bar": "barz"
}
}
Over the top
The other way is to define a GDB pretty printer in python and make it tightly associated to your project (autoloading stuff activated). See this link for an in-depth approach.
Basically, when in gdb you would type:
(gdb) p foo
and GDB will automagically test for foo
's type and invoke the associated pretty printer if any. That would end-up in the same result. The main difference is that it is done using the well-known print
command. The person debugging would not have to learn a new command (like the pjson
defined in the short answer).
Quoting:
A pretty-printer consists of two parts: a lookup function to detect if the type is supported, and the printer itself.
Here is an example showing how a
std::string
printer might be written. See Pretty Printing API, for details on the API this class must provide.
class StdStringPrinter(object):
"Print a std::string"
def __init__(self, val):
self.val = val
def to_string(self):
return self.val['_M_dataplus']['_M_p']
def display_hint(self):
return 'string'
Still quoting for the sake of completness:
And here is an example showing how a lookup function for the printer example above might be written.
def str_lookup_function(val):
lookup_tag = val.type.tag
if lookup_tag == None:
return None
regex = re.compile("^std::basic_string<char,.*>$")
if regex.match(lookup_tag):
return StdStringPrinter(val)
return None
That looks pretty useful. Unfortunately I am out of votes ATM.
– πάντα ῥεῖ
6 hours ago
add a comment |
I found my own answer reading further the GDB capabilities and stack overflow questions concerning print of std::string.
Short path
I simply defined a gdb command as follows:
# this is a gdb script
# can be loaded from gdb using
# source my_script.txt (or. gdb or whatever you like)
define pjson
# use the lohmann's builtin dump method, ident 4 and use space separator
printf "%sn", $arg0.dump(4, ' ', true).c_str()
end
# configure command helper (text displayed when typing 'help pjson' in gdb)
document pjson
Prints a lohmann's JSON C++ variable as a human-readable JSON string
end
Using it in gdb:
(gdb) source my_custom_script.gdb
(gdb) pjson foo
{
"flex" : 0.2,
"awesome_str": "bleh",
"nested": {
"bar": "barz"
}
}
Over the top
The other way is to define a GDB pretty printer in python and make it tightly associated to your project (autoloading stuff activated). See this link for an in-depth approach.
Basically, when in gdb you would type:
(gdb) p foo
and GDB will automagically test for foo
's type and invoke the associated pretty printer if any. That would end-up in the same result. The main difference is that it is done using the well-known print
command. The person debugging would not have to learn a new command (like the pjson
defined in the short answer).
Quoting:
A pretty-printer consists of two parts: a lookup function to detect if the type is supported, and the printer itself.
Here is an example showing how a
std::string
printer might be written. See Pretty Printing API, for details on the API this class must provide.
class StdStringPrinter(object):
"Print a std::string"
def __init__(self, val):
self.val = val
def to_string(self):
return self.val['_M_dataplus']['_M_p']
def display_hint(self):
return 'string'
Still quoting for the sake of completness:
And here is an example showing how a lookup function for the printer example above might be written.
def str_lookup_function(val):
lookup_tag = val.type.tag
if lookup_tag == None:
return None
regex = re.compile("^std::basic_string<char,.*>$")
if regex.match(lookup_tag):
return StdStringPrinter(val)
return None
That looks pretty useful. Unfortunately I am out of votes ATM.
– πάντα ῥεῖ
6 hours ago
add a comment |
I found my own answer reading further the GDB capabilities and stack overflow questions concerning print of std::string.
Short path
I simply defined a gdb command as follows:
# this is a gdb script
# can be loaded from gdb using
# source my_script.txt (or. gdb or whatever you like)
define pjson
# use the lohmann's builtin dump method, ident 4 and use space separator
printf "%sn", $arg0.dump(4, ' ', true).c_str()
end
# configure command helper (text displayed when typing 'help pjson' in gdb)
document pjson
Prints a lohmann's JSON C++ variable as a human-readable JSON string
end
Using it in gdb:
(gdb) source my_custom_script.gdb
(gdb) pjson foo
{
"flex" : 0.2,
"awesome_str": "bleh",
"nested": {
"bar": "barz"
}
}
Over the top
The other way is to define a GDB pretty printer in python and make it tightly associated to your project (autoloading stuff activated). See this link for an in-depth approach.
Basically, when in gdb you would type:
(gdb) p foo
and GDB will automagically test for foo
's type and invoke the associated pretty printer if any. That would end-up in the same result. The main difference is that it is done using the well-known print
command. The person debugging would not have to learn a new command (like the pjson
defined in the short answer).
Quoting:
A pretty-printer consists of two parts: a lookup function to detect if the type is supported, and the printer itself.
Here is an example showing how a
std::string
printer might be written. See Pretty Printing API, for details on the API this class must provide.
class StdStringPrinter(object):
"Print a std::string"
def __init__(self, val):
self.val = val
def to_string(self):
return self.val['_M_dataplus']['_M_p']
def display_hint(self):
return 'string'
Still quoting for the sake of completness:
And here is an example showing how a lookup function for the printer example above might be written.
def str_lookup_function(val):
lookup_tag = val.type.tag
if lookup_tag == None:
return None
regex = re.compile("^std::basic_string<char,.*>$")
if regex.match(lookup_tag):
return StdStringPrinter(val)
return None
I found my own answer reading further the GDB capabilities and stack overflow questions concerning print of std::string.
Short path
I simply defined a gdb command as follows:
# this is a gdb script
# can be loaded from gdb using
# source my_script.txt (or. gdb or whatever you like)
define pjson
# use the lohmann's builtin dump method, ident 4 and use space separator
printf "%sn", $arg0.dump(4, ' ', true).c_str()
end
# configure command helper (text displayed when typing 'help pjson' in gdb)
document pjson
Prints a lohmann's JSON C++ variable as a human-readable JSON string
end
Using it in gdb:
(gdb) source my_custom_script.gdb
(gdb) pjson foo
{
"flex" : 0.2,
"awesome_str": "bleh",
"nested": {
"bar": "barz"
}
}
Over the top
The other way is to define a GDB pretty printer in python and make it tightly associated to your project (autoloading stuff activated). See this link for an in-depth approach.
Basically, when in gdb you would type:
(gdb) p foo
and GDB will automagically test for foo
's type and invoke the associated pretty printer if any. That would end-up in the same result. The main difference is that it is done using the well-known print
command. The person debugging would not have to learn a new command (like the pjson
defined in the short answer).
Quoting:
A pretty-printer consists of two parts: a lookup function to detect if the type is supported, and the printer itself.
Here is an example showing how a
std::string
printer might be written. See Pretty Printing API, for details on the API this class must provide.
class StdStringPrinter(object):
"Print a std::string"
def __init__(self, val):
self.val = val
def to_string(self):
return self.val['_M_dataplus']['_M_p']
def display_hint(self):
return 'string'
Still quoting for the sake of completness:
And here is an example showing how a lookup function for the printer example above might be written.
def str_lookup_function(val):
lookup_tag = val.type.tag
if lookup_tag == None:
return None
regex = re.compile("^std::basic_string<char,.*>$")
if regex.match(lookup_tag):
return StdStringPrinter(val)
return None
edited 1 hour ago
answered 7 hours ago
LoneWandererLoneWanderer
1,122825
1,122825
That looks pretty useful. Unfortunately I am out of votes ATM.
– πάντα ῥεῖ
6 hours ago
add a comment |
That looks pretty useful. Unfortunately I am out of votes ATM.
– πάντα ῥεῖ
6 hours ago
That looks pretty useful. Unfortunately I am out of votes ATM.
– πάντα ῥεῖ
6 hours ago
That looks pretty useful. Unfortunately I am out of votes ATM.
– πάντα ῥεῖ
6 hours ago
add a comment |
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You mean you don't find great joy manually digging through red/black trees to try and find something? ;)
– Retired Ninja
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