C语言 如何从被调用函数更改调用函数中的变量？
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原文地址: http://stackoverflow.com/questions/3377158/
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How to change a variable in a calling function from a called function?
提问by kaka
How should the try()function be modified (and it's call) to get the output as 11 from the program below?
应如何try()修改该函数（及其调用）以从下面的程序中获得 11 的输出？
#include <stdio.h>
/* declare try() here */
int main(void)
{
int x = 10;
try(); /* Call can change */
printf("%d\n", x);
return 0;
}
void try() /* Signature can change */
{
/* how to change x here?? */
}
回答by Jeff Mercado
To change the value of xfrom within a function, have try()take a pointer to the variable and change it there.
要从x函数内部更改 的值，请try()获取指向变量的指针并在那里更改它。
e.g.,
例如，
void try(int *x)
{
*x = 11;
}
int main()
{
int x = 10;
try(&x);
printf("%d",x);
return 0;
}
回答by Merlyn Morgan-Graham
The other answers are correct. The only way to truly change a variable inside another function is to pass it via pointer. Jeff M's example is the best, here.
其他答案都是正确的。真正改变另一个函数内的变量的唯一方法是通过指针传递它。Jeff M 的例子是最好的，在这里。
If it doesn't really have to be that exact same variable, you can return the value from that function, and re-assign it to the variable, ala:
如果它实际上不必是完全相同的变量，则可以从该函数返回值，然后将其重新分配给变量 ala：
int try(int x)
{
x = x + 1;
return x;
}
int main()
{
int x = 10;
x = try(x);
printf("%d",x);
return 0;
}
Another option is to make it global (but don't do this very often - it is extremely messy!):
另一种选择是将其设为全局（但不要经常这样做 - 它非常混乱！）：
int x;
void try()
{
x = 5;
}
int main()
{
x = 10;
try();
printf("%d",x);
return 0;
}
回答by Ed S.
You need to pass a pointer to the memory location (a copy of the original pointer). Otherwise you are just modifying a copy of the original value which is gone when the function exits.
您需要传递一个指向内存位置的指针（原始指针的副本）。否则，您只是在修改函数退出时消失的原始值的副本。
void Try( int *x );
int main( void )
{
int x = 10;
Try( &x );
/* ... */
}
void Try( int *x )
{
*x = 11;
}
