考虑一个简单的Python函数:

def gen():
    for i in range(10):
        yield i

是否有可能在C或者C++中实现呢?

Coroutines in C一文中详细的介绍了在C语言中实现的可能性。

现在简单介绍下:

版本1:

int gen(void) {
    static int i, state = 0;
    switch (state) {
        case 0: goto LABEL0;
        case 1: goto LABEL1;
    }
    LABEL0: /* start of function */
    for (i = 0; i < 10; i++) {
         state = 1; /* so we will come back to LABEL1 */
        return i;
        LABEL1:; /* resume control straight after the return */
    }
}

版本2:

int gen(void) {
    static int i, state = 0;
    switch (state) {
        case 0: /* start of function */
        for (i = 0; i < 10; i++) {
            state = 1; /* so we will come back to "case 1" */
            return i;
            case 1:; /* resume control straight after the return */
        }
    }
}

版本3:

#define crBegin static int state=0; switch(state) { case 0:
#define crReturn(i,x) do { state=i; return x; case i:; } while (0)
#define crFinish }
int gen(void) {
    static int i;
    crBegin;
    for (i = 0; i < 10; i++)
        crReturn(1, i);
    crFinish;
}

版本4:

#define crBegin static int state=0; switch(state) { case 0:
#define crReturn(x) do { state=__LINE__; return x; 
    case __LINE__:; } while (0)
#define crFinish }
int gen(void) {
    static int i;
    crBegin;
    for (i = 0; i < 10; i++)
        crReturn(i);
    crFinish;
}

对于C++,在boost库中,有专门的实现:
Boost.Coroutine
该库的部分实现使用了汇编语言。

本文固定链接: http://www.js-code.com/cpp/cpp_59066.html