In which language should I code conditional breakpoints in gdb?

Question

I'm very confused about conditional breakpoints in gdb.

Recently, I wanted to put a breakpoint which breaks when a specific variable is equal to "foo" in a C++ program.

To do that I typed this in the gdb CLI :

break LINE_NUMBER if strcmp(myVar, "foo") == 0

but it took me a very long time and a lot of tries to find how to code it.

I've first started with :

break LINE_NUMBER if myVar == "foo"

break LINE_NUMBER if myVar.c_str() == "foo"

...

before I finally found out conditional breakpoints MAY have to be programmed in C.

Anyone knows where the rules to code conditional breakpoints are written ?

I've read the documentation but didn't find the info I needed...

https://sourceware.org/gdb/current/onlinedocs/gdb.html/Conditions.html#Conditions

Answer 1

Documentation explicitly states that a condition is a Boolean expression in your programming language:

You can also specify a condition for a breakpoint. A condition is just a Boolean expression in your programming language (see Expressions).

Your program is written in C++ so in theory any valid C++ Boolean expression should work. But in practice GDB has a limited support of C++ expressions, only some subset of them works, strcmp(myVar, "foo") == 0 is one of the examples which works. You can find some areas of improvement on Expression Evaluation on GDB Wiki.