Debugging C Plus Plus (Debugging with GDB)
220.127.116.11 GDB Features for C++
Some GDB commands are particularly useful with C++, and some are designed specifically for use with C++. Here is a summary:
When you want a breakpoint in a function whose name is overloaded, GDB has the capability to display a menu of possible breakpoint locations to help you specify which function definition you want. See Ambiguous Expressions.
Setting breakpoints using regular expressions is helpful for setting breakpoints on overloaded functions that are not members of any special classes. See Setting Breakpoints.
Debug C++ exception handling using these commands. See Setting Catchpoints.
Print inheritance relationships as well as other information for type
typename. See Examining the Symbol Table.
info vtbl expression.
info vtbl command can be used to display the virtual method tables of the object computed by
expression. This shows one entry per virtual table; there may be multiple virtual tables when multiple inheritance is in use.
name. See Symbols, for a more complete description of the
set print demangle
show print demangle
set print asm-demangle
show print asm-demangle
Control whether C++ symbols display in their source form, both when displaying code as C++ source and when displaying disassemblies. See Print Settings.
set print object
show print object
Choose whether to print derived (actual) or declared types of objects. See Print Settings.
set print vtbl
show print vtbl
Control the format for printing virtual function tables. See Print Settings. (The
vtbl commands do not work on programs compiled with the HP ANSI C++ compiler (
set overload-resolution on
Enable overload resolution for C++ expression evaluation. The default is on. For overloaded functions, GDB evaluates the arguments and searches for a function whose signature matches the argument types, using the standard C++ conversion rules (see C++ Expressions, for details). If it cannot find a match, it emits a message.
set overload-resolution off
Disable overload resolution for C++ expression evaluation. For overloaded functions that are not class member functions, GDB chooses the first function of the specified name that it finds in the symbol table, whether or not its arguments are of the correct type. For overloaded functions that are class member functions, GDB searches for a function whose signature exactly matches the argument types.
Show the current setting of overload resolution.
Overloaded symbol names
You can specify a particular definition of an overloaded symbol, using the same notation that is used to declare such symbols in C++: type
symbol(types) rather than just
symbol. You can also use the GDB command-line word completion facilities to list the available choices, or to finish the type list for you. See Command Completion, for details on how to do this.
Breakpoints in functions with ABI tags
The GNU C++ compiler introduced the notion of ABI “tags”, which correspond to changes in the ABI of a type, function, or variable that would not otherwise be reflected in a mangled name. See https://developers.redhat.com/blog/2015/02/05/gcc5-and-the-c11-abi/ for more detail.
The ABI tags are visible in C++ demangled names. For example, a function that returns a std::string:
when compiled for the C++11 ABI is marked with the
cxx11 ABI tag, and GDB displays the symbol like this:
You can set a breakpoint on such functions simply as if they had no tag. For example:
(gdb) b function(int) Breakpoint 2 at 0x40060d: file main.cc, line 10. (gdb) info breakpoints Num Type Disp Enb Address What 1 breakpoint keep y 0x0040060d in function[abi:cxx11](int) at main.cc:10
On the rare occasion you need to disambiguate between different ABI tags, you can do so by simply including the ABI tag in the function name, like:
(gdb) b ambiguous[abi:other_tag](int)