Debugging with GDB (September 2007)

80 Debugging with GDB

‘.f’

‘.F’

‘.f90’ Fortran source ﬁle. GDB does not distinguish between Fortran 77 and Fortran

90 ﬁles.

‘.s’

‘.S’ Assembler source ﬁle. This actually behaves almost like C, but GDB does not

skip over function prologues when stepping.

In addition, you may set the language associated with a ﬁlename extension. See Sec-

tion 9.2 [Displaying the language], page 80.

9.1.2 Setting the working language

If you allow GDB to set the language automatically, expressions are interpreted the same

way in your debugging session and your program.

If you wish, you may set the language manually. To do this, issue the command ‘set

language lang ’, where lang is the name of a language, such as c. For a list of the supported

languages, type ‘set language’.

Setting the language manually prevents GDB from updating the working language au-

tomatically. This can le ad to confusion if you try to debug a program when the working

language is not the same as the source language, when an expression is acceptable to both

languages—but means diﬀerent things. For instance, if the current source ﬁle were written

in C, and GDB was parsing Mo dula-2, a command such as:

print a = b + c

might not have the eﬀect you intended. In C, this means to add b and c and place the

result in a. The result printed would be the value of a. In Modula-2, this means to compare

a to the result of b+c, yielding a BOOLEAN value.

9.1.3 Having GDB infer the source language

To have GDB set the working language automatically, use ‘set language local’ or ‘set

language auto’. GDB then infers the working language. That is, when your program stops

in a frame (usually by encountering a breakpoint), GDB sets the working language to the

language recorded for the function in that frame. If the language for a frame is unknown

(that is, if the function or block corresponding to the frame was deﬁned in a source ﬁle that

does not have a recognized extension), the current working language is not changed, and

GDB issues a warning.

This may not seem necessary for most programs, which are written entirely in one source

language. However, program modules and libraries written in one source language can be

used by a main program written in a diﬀerent source language. Using ‘set language auto’

in this case frees you from having to set the working language manually.

9.2 Displaying the language

The following commands help you ﬁnd out which language is the working language, and

also what language source ﬁles were written in.