在Makefile中做什么？

通过查看我的

Makefile

，我看到了

SOMEVAR？=somestuff

，我不确定这是什么意思

任何帮助都将不胜感激

---

谢谢

根据，仅当当前未使用其他值定义时，才会设置

SOMEVAR

。

根据，仅当当前未使用其他值定义时，才会设置

SOMEVAR

。

如果尚未定义，则将值分配给

SOMEVAR

。

如果尚未定义，则将值分配给

SOMEVAR

。

请参阅

make

的手册页：

变量赋值 make中的变量与shell中的变量非常相似，而且，tradi- 字符，由所有大写字母组成

变量赋值修饰符 可用于为变量赋值的五个运算符如下 如下:

 =       Assign the value to the variable.  Any previous value is overrid-
         den.

 +=      Append the value to the current value of the variable.

 ?=      Assign the value to the variable if it is not already defined.

 :=      Assign with expansion, i.e. expand the value before assigning it
         to the variable.  Normally, expansion is not done until the vari-
         able is referenced.  NOTE: References to undefined variables are
         not expanded.  This can cause problems when variable modifiers
         are used.

 !=      Expand the value and pass it to the shell for execution and
         assign the result to the variable.  Any newlines in the result
         are replaced with spaces.

---

请参阅

make

的手册页：

变量赋值 make中的变量与shell中的变量非常相似，而且，tradi- 字符，由所有大写字母组成

变量赋值修饰符 可用于为变量赋值的五个运算符如下 如下:

 =       Assign the value to the variable.  Any previous value is overrid-
         den.

 +=      Append the value to the current value of the variable.

 ?=      Assign the value to the variable if it is not already defined.

 :=      Assign with expansion, i.e. expand the value before assigning it
         to the variable.  Normally, expansion is not done until the vari-
         able is referenced.  NOTE: References to undefined variables are
         not expanded.  This can cause problems when variable modifiers
         are used.

 !=      Expand the value and pass it to the shell for execution and
         assign the result to the variable.  Any newlines in the result
         are replaced with spaces.