Question

需要一些快速帮助。这是一个大学程序，一切都工作正常，除非我调用my：forLoop方法迭代100个数字（1,1,100）从1开始1到100然后进行迭代％5（i %% 5）。由于某种原因，我不能让这个工作。感谢任何帮助或指导。

当我回显%% A时，它会遍历所有数字完美。当我回显％结果％时，我得到一个空白的“”（内部没有）

:forLoop
FOR /L %%A IN (1,1,100) DO (
set /A result=%%A %% 2
echo "%%A"
echo "%result%"
)

正确的代码是

:forLoop
setlocal ENABLEDELAYEDEXPANSION
FOR /L %%A IN (1,1,100) DO (
set /A result=%%A %% 5
echo !result! >> results.txt
set /A total=!total!+!result!
echo !total!
)

Answer 1

问题是当%result%被读取时for被替换，这意味着它在循环执行时不再是变量。您需要启用延迟变量扩展，然后使用!代替%：

setlocal ENABLEDELAYEDEXPANSION

:forLoop
FOR /L %%A IN (1,1,100) DO (
set /A result=%%A %% 5
echo "%%A"
echo !result!
)

在运行SET /?时收到的帮助信息中对此进行了解释：

Delayed environment variable expansion is useful for getting around
the limitations of the current expansion which happens when a line
of text is read, not when it is executed.  The following example
demonstrates the problem with immediate variable expansion:

    set VAR=before
    if "%VAR%" == "before" (
        set VAR=after
        if "%VAR%" == "after" @echo If you see this, it worked
    )

would never display the message, since the %VAR% in BOTH IF statements
is substituted when the first IF statement is read, since it logically
includes the body of the IF, which is a compound statement.  So the
IF inside the compound statement is really comparing "before" with
"after" which will never be equal.  Similarly, the following example
will not work as expected:

    set LIST=
    for %i in (*) do set LIST=%LIST% %i
    echo %LIST%

in that it will NOT build up a list of files in the current directory,
but instead will just set the LIST variable to the last file found.
Again, this is because the %LIST% is expanded just once when the
FOR statement is read, and at that time the LIST variable is empty.
So the actual FOR loop we are executing is:

    for %i in (*) do set LIST= %i

which just keeps setting LIST to the last file found.

Delayed environment variable expansion allows you to use a different
character (the exclamation mark) to expand environment variables at
execution time.  If delayed variable expansion is enabled, the above
examples could be written as follows to work as intended:

    set VAR=before
    if "%VAR%" == "before" (
        set VAR=after
        if "!VAR!" == "after" @echo If you see this, it worked
    )

    set LIST=
    for %i in (*) do set LIST=!LIST! %i
    echo %LIST%

Windows批处理脚本 - 对于/ L不起作用 - 简单

1 个答案: