一个棘手的 GNU make 问题

发布于 2024-11-29 02:50:13 字数 467 浏览 2 评论 0原文

下面是我希望 makefile 执行的一些伪代码：

if (A doesn't exist) or (B is newer than A):
    rm -rf A
    create an empty A
parallel_for X in (a large set of files):
    if (X is newer than A):
        update A using the contents of X

在上面的伪代码中，A 是一个 SQLite 数据库，B 是一个 C 头文件，并且中的每个文件“大文件集”是一个 C 源文件。

基本上，如果我只修改其中一个C源文件，我只是希望数据库能够快速更新，而不是从头开始重建整个数据库。

这种类型的问题可以直接在 GNU make 中解决吗，还是我必须求助于使用脚本？

提前致谢！

原文

Here's some pseudocode for what I want my makefile to do:

if (A doesn't exist) or (B is newer than A):
    rm -rf A
    create an empty A
parallel_for X in (a large set of files):
    if (X is newer than A):
        update A using the contents of X

In the above pseudocode, A is an SQLite database, B is a C header file, and each of the files in the "large set of files" is a C source file.

Basically, if I only modify one of the C source files, I just want the database to be quickly updated rather than rebuilding the entire database from scratch.

Is this type of problem solvable directly in GNU make, or am I going to have to resort to using a script?

Thanks in advance!

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镜花水月 2024-12-06 02:50:13

像这样的东西应该可以工作：

A:: B
        -rm -f $@
        create_A $@

A:: $(all_X)
        update_A_from_Xes $@ $?

$? 扩展到比 A 更新的 $(all_X) 子集（请参阅“自动变量部分的 GNU Make 手册了解更多详细信息）。必须针对所有后续参数更新其第一个参数；它只会被调用一次

。 href="http://www.gnu.org/software/make/manual/html_node/Double_002dColon.html" rel="noreferrer">双冒号告诉 Make 运行更新 A 的命令是不同的它相对于 B 来说已经过时了，而对于 Xes 来说已经过时了，我不确定如果两者都已过时，这两组命令是否都会运行；运行时，A::B 规则将首先运行。

Something like this ought to work:

A:: B
        -rm -f $@
        create_A $@

A:: $(all_X)
        update_A_from_Xes $@ $?

$? expands to the subset of $(all_X) that are newer than A (see the "Automatic Variables section of the GNU Make manual for more details). Therefore, update_A_from_Xes must update its first argument with respect to all of the subsequent arguments; it will only be invoked once.

The double colons tell Make that the commands to run to update A are different when it's out of date with respect to B than when it's out of date with respect to the Xes. I am not sure whether both sets of commands will get run in the case that it is out of date with respect to both; if they do both get run, the A:: B rules will get run first.

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