我正在尝试为作为结构成员的并集成员分配值,但似乎未分配该值。
我已经完成了程序,在分配之后,len_param.data
值似乎是某种指针(请参阅文章末尾的GDB输出)
此外,如果我printf
,它可以正常运行:
len_param.data.v_int = 4;
// If I uncomment this line, IT RUNS FINE! WHY?
// printf("len_param.data.v_int: %i \n", len_param.data.v_int);
len_param
的类型如下:
struct Parameter {
enum {
NORMAL, ARRAY, SKIP,
} type;
GIDirection direction;
GIArgument data;
};
和GIArgument
定义:
union _GIArgument
{
gboolean v_boolean;
gint8 v_int8;
guint8 v_uint8;
gint16 v_int16;
guint16 v_uint16;
gint32 v_int32;
guint32 v_uint32;
gint64 v_int64;
guint64 v_uint64;
gfloat v_float;
gdouble v_double;
gshort v_short;
gushort v_ushort;
gint v_int;
guint v_uint;
glong v_long;
gulong v_ulong;
gssize v_ssize;
gsize v_size;
gchar * v_string;
gpointer v_pointer;
};
typedef _GIArgument GIArgument;
完整的文件可以在这里找到:https://gist.github.com/romgrk/642388914a9ff412eb5683fca44009d7#file-function-cc-L255
我在那一步走的时候的GDB输出是:
Thread 1 "node" hit Breakpoint 1, GNodeJS::FunctionInvoker (info=...) at ../src/function.cc:256
256 len_param.data.v_int = GetV8ArrayLength(info[in_arg]);
(gdb) step
GNodeJS::GetV8ArrayLength (value=...) at ../src/function.cc:25
25 static int GetV8ArrayLength (Local<Value> value) {
(gdb) finish
Run till exit from #0 GNodeJS::GetV8ArrayLength (value=...) at ../src/function.cc:25
GNodeJS::FunctionInvoker (info=...) at ../src/function.cc:260
260 callable_arg_values[length_i].v_pointer = &len_param.data;
Value returned is $1 = 4
(gdb) p len_param.data.v_int
$2 = -17928
(gdb) p len_param
$3 = {
type = GNodeJS::Parameter::SKIP,
direction = GI_DIRECTION_INOUT,
data = {
v_boolean = -17928,
v_int8 = -8 '\370',
v_uint8 = 248 '\370',
v_int16 = -17928,
v_uint16 = 47608,
v_int32 = -17928,
v_uint32 = 4294949368,
v_int64 = 140737488337400,
v_uint64 = 140737488337400,
v_float = -nan(0x7fb9f8),
v_double = 6.9533558069492434e-310,
v_short = -17928,
v_ushort = 47608,
v_int = -17928,
v_uint = 4294949368,
v_long = 140737488337400,
v_ulong = 140737488337400,
v_ssize = 140737488337400,
v_size = 140737488337400,
v_string = 0x7fffffffb9f8 "\t\357\304\303J\a",
v_pointer = 0x7fffffffb9f8
}
}
答案 0 :(得分:1)
问题可能是,len_param.data
除了在范围之外和len_param
的生存期到期之前立即获取地址之外,什么也没做。因此,编译器认为没有必要在其中存储任何内容。
下面是定义,使用和死亡len_param
的代码段(省略了不必要的代码,并添加了一些注释注释):
if (param.type == Parameter::ARRAY) {
// ...
Parameter len_param = call_parameters[length_i]; // len_param is defined
if (len_param.direction == GI_DIRECTION_IN) {
// ...
}
else if (len_param.direction == GI_DIRECTION_INOUT) {
len_param.data.v_int = GetV8ArrayLength(info[in_arg]);
callable_arg_values[length_i].v_pointer = &len_param.data;
}
} // len_param goes out of scope, so it's no longer alive
// and the pointer that got placed in `callable_arg_values[length_i].v_pointer`
// is pointing to garbage
根本问题是callable_arg_values[length_i].v_pointer
中的指针在存储之后是无效的。