Debugging with GDB: Debugging C Plus Plus

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15.4.1.7 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:

breakpoint menus

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.

rbreak regex

Setting breakpoints using regular expressions is helpful for setting breakpoints on overloaded functions that are not members of any special classes. See Setting Breakpoints.

catch throw

catch rethrow

catch catch

Debug C++ exception handling using these commands. See Setting Catchpoints.

ptype typename

Print inheritance relationships as well as other information for type typename. See Examining the Symbol Table.

info vtbl expression.

The 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.

demangle name

Demangle name. See Symbols, for a more complete description of the demangle command.

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 (aCC).)

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 overload-resolution

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:

std::string function(int);

when compiled for the C++11 ABI is marked with the cxx11 ABI tag, and GDB displays the symbol like this:

function[abi:cxx11](int)

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)

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