duan032225 2019-05-29 03:51
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CGO中的C NULL类型

I have a C function that returns NULL when an exception occurs. How can I check whether the returned value is NULL or not in Go since it has no built-in types to represent C NULL. Below is my code

retVal := C.myfunc()

if retVal == nil {
  // handle the error
}

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  • douchun1900 2019-05-29 06:05
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    I think you can use nil to test if the c function returns NULL. Try the following code:

    package main
    
    /*
    #include <stdio.h>
    #include <stdlib.h>
    
    int* cfunc(int i) {
        if (i == 0) {
            return NULL;
        }
    
        int *p = (int*)malloc(sizeof(int));
        *p = 100;
        return p;
    }
    */
    import "C"
    
    import "fmt"
    import "unsafe"
    
    func call_cfunc(i int32) {
        ret := C.cfunc(C.int(i))
        if ret == nil {
            fmt.Println("nil")
        } else {
            fmt.Println(*ret)
            C.free(unsafe.Pointer(ret))
        }
    }
    
    func main() {
        call_cfunc(0)
        call_cfunc(1)
    }
    
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