...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
In addition to generic error messages, bjam
may emit one
of the following:
warning: unknown rule X
A rule was invoked that has not been defined with an "actions
"
or "rule
" statement.
using N temp target(s)
Targets marked as being temporary (but nonetheless present) have been found.
updating N target(s)
Targets are out-of-date and will be updated.
can't find N target(s)
Source files can't be found and there are no actions to create them.
can't make N target(s)
Due to sources not being found, other targets cannot be made.
warning: X depends on itself
A target depends on itself either directly or through its sources.
don't know how to make X
A target is not present and no actions have been defined to create it.
X skipped for lack of Y
A source failed to build, and thus a target cannot be built.
warning: using independent target X
A target that is not a dependency of any other target is being referenced
with $(<)
or $(>)
.
X removed
BJam
removed a partially built target after being interrupted.
For parallel building to be successful, the dependencies among files must
be properly spelled out, as targets tend to get built in a quickest-first
ordering. Also, beware of un-parallelizable commands that drop fixed-named
files into the current directory, like yacc(1)
does.
A poorly set $(JAMSHELL)
is likely to result in silent
failure.
This section is derived from the official Jam documentation and from experience using it and reading the Jambase rules. We repeat the information here mostly because it is essential to understanding and using Jam, but is not consolidated in a single place. Some of it is missing from the official documentation altogether. We hope it will be useful to anyone wishing to become familiar with Jam and the Boost build system.
rules
" are actually simple procedural
entities. Think of them as functions. Arguments are separated by colons.
DEPENDS
rule creates
a link in the dependency graph between the named targets.
INCLUDES
rule is incorrect: INCLUDES targets1 : targets2
causes everything that depends on a member of targets1
to depend on all members of targets2. It does this
in an odd way, by tacking targets2 onto a special
tail section in the dependency list of everything in targets1.
It seems to be OK to create circular dependencies this way; in fact, it
appears to be the "right thing to do" when a single build action
produces both targets1 and targets2.
actions
declared
with the same name as the rule, the actions are added to the updating actions
for the target identified by the rule's first argument. It is actually
possible to invoke an undeclared rule if corresponding actions are declared:
the rule is treated as empty.
NOTFILE
targets) are associated
with paths in the file system through a process called binding. Binding
is a process of searching for a file with the same name as the target (sans
grist), based on the settings of the target-specific SEARCH
and LOCATE
variables.
on
a target. Target-specific variable values can usually
not be read, and take effect only in the following contexts:
on
the target named by the first argument (the target being updated).
Because Jam builds its entire dependency tree before executing actions,
Jam rules make target-specific variable settings as a way of supplying
parameters to the corresponding actions.
SEARCH
and LOCATE
variables, as described here.
on
the target named by the rule's
first argument (the source file being scanned).
bind
action modifier.
test.exe
" may
be used by targets in separate subprojects, or for the debug and release
variants of the "same" abstract target. Each distinct target
bound to a file called "test.exe" has its own unique grist prefix.
The Boost build system also takes full advantage of Jam's ability to divide
strings on grist boundaries, sometimes concatenating multiple gristed elements
at the beginning of a string. Grist is used instead of identifying targets
with absolute paths for two reasons:
MESSAGE ?\= starting jam... ; if #(MESSAGE) { ECHO The message is: #(MESSAGE) ; }If the user wants a specific message, he invokes jam with
"-sMESSAGE=message
text"
. If he wants no message, he invokes jam with -sMESSAGE=
and nothing at all is printed.
-xvalue
, and
-x value
.