如何将结构的字段名称作为参数传递？ [英] How to pass the field name of a struct as a parameter?
问题描述
有一些sturct数组（或结构向量），例如：
struct S1_t
{
双keyField;
..//其他字段
}
S1_t s1 [100];
std :: vector< S1_t> vecS1;
我需要在数组中找到项目的索引s1或者矢量vecS1
在字段keyField中具有最小值。
某些代码可能是：
// --------------------------------------- -------
double minvalue = s1 [0];
for（int i = 0; i< 100; i ++）// for（int i = 0; i< vecS1.size（）; i ++）
....
{
if（s1 [ i] .keyField< minvalue）
{
minvalue = s1 [i] .keyField;
index = i;
}
}
// -------------------------- --------------------
但是，因为有很多这样的数组（向量）有不同的
结构类型
（所以，使用不同的字段名称）
我如何定义一个函数（或MACRO？）来获取index
minumal项目（通过比较关键字段的值）？
如MIN（struct_array_variable，field_name）
例如
index = MI N（s1，keyField）;
获取数组的索引s1最小值为keyField。
并且，
index = MIN（s2，f2）得到s2 ; （定义如下:)
struct s2_t
{
int f2;
//其他领域
}
s2_t s2 [100]
一个类似的函数是FIND（struct_array，field，value）
从数组中找到索引struct_array，其中
struct_array [index] .field == value;
我认为关键是如何将字段名称
作为参数传递？不是吗？
有人能帮帮我吗？
非常感谢你！
Jellicle写道：有一些sturct数组（或结构向量），例如：
struct S1_t
{
双键字段;
..//其他字段
S1_t s1 [100];
标准::矢量<&S1_T GT; vecS1;
我需要在数组s1中找到项目的索引。或者矢量vecS1
其中
在字段keyField中具有最小值。
有些代码可以是：
// ----- -----------------------------------------
双倍minvalue = s1 [0];
你的意思是
double minvalue = s1 [0] .keyField;
??
for（int i = 0; i< 100; i ++）// for（int i = 0; i< vecS1.size（）; i ++）
你的意思是
for（int i = 1; i< ...
??
......
{
if（s1 [i] .keyField< minvalue）
{/ / minvalue = s1 [i] .keyField;
index = i;
}
}
// ---------------------------------- ------------
然而，由于有许多这样的数组（向量）具有不同的结构类型
（因此，具有不同的结构类型）字段名称
如何定义一个函数（或MACRO？）来获取minumal项的索引（通过比较关键字段的值）？
如MIN（struct_array_variable，field_name）
索引= MIN（s1，keyField）;
获取数组的索引s1，机智h最小值为keyField。
index = MIN（s2，f2）得到s2的值。 （定义如下:)
struct s2_t
{//} int f2;
//其他领域
}
s2_t s2 [100]
类似的函数是FIND（struct_array，field，value）
从数组struct_array中查找索引。
struct_array [index] .field == value;
我认为关键是如何将字段名称
作为参数传递？不是吗？
不，不是。关键点是要了解指向
成员以及如何使用它们的指示。
V
-
请在通过电子邮件回复时删除资金''A'
我没有回复最热门的回复，请不要问
你可以使用以下
众所周知的技巧获得结构中字段f的偏移量：
#define OFFSET（s，f）&（（struct s *）0） - > f
一旦有了偏移量，就可以直接解决问题了。 />
-Shimin
Jellicle写道：有一些sturct数组（或结构向量），例如： br />
struct S1_t
{
其他领域
}
S1_t s1 [100];
std :: vector< S1_t> vecS1;
我需要在数组s1中找到项目的索引。或者矢量vecS1
其中
在字段keyField中具有最小值。
有些代码可以是：
// ----- -----------------------------------------
双倍minvalue = s1 [0];
for（int i = 0; i< 100; i ++）// for（int i = 0; i< vecS1.size（）; i ++）
...
{
if（s1 [i] .keyField< minvalue）
{/ / minvalue = s1 [i] .keyField;
index = i;
}
}
// ------------------------------------- ---------
但是，因为有许多这样的数组（向量）具有不同的结构类型
（因此，具有不同的字段名称）
如何定义一个函数（或MACRO？）来获取minumal项目的索引（通过比较关键字段的值）？
如MIN（struct_array_variable，field_name）
索引= MIN（s1，keyField）;
获取数组索引s1具有最小值keyField。
index = MIN（s2，f2）得到s2的值。 （定义如下:)
struct s2_t
{//} int f2;
//其他领域
}
s2_t s2 [100]
类似的函数是FIND（struct_array，field，value）
从数组struct_array中查找索引。
struct_array [index] .field == value;
我认为关键是如何将字段名称
作为参数传递？不是吗？
任何人都可以帮助我吗？
非常感谢！
Victor Bazarov写道：
Jellicle写道：
有些代码可能是：
// --------------------------------------------- -
double minvalue = s1 [0];
你的意思是
double minvalue = s1 [0] .keyField; <
for（int i = 0; i< 100; i ++）// for（int i = 0; i< vecS1.size（） ; i ++）
你的意思是
for（int i = 1; i< ...
??
你是对的:-)。
（我应该检查矢量中是否存在vecS1 [0] :-)）
但令我困惑的是如何处理各种类型的不同数组或向量中的
结构和字段。
There are some sturct arrays (or struct vectors), such as:
struct S1_t
{
double keyField ;
..// other fields
}
S1_t s1[100];
std::vector<S1_t> vecS1;
I need to find the index of the item in array "s1" or vector "vecS1"
which
has the minimal value in field "keyField".
Some codes could be:
//----------------------------------------------
double minvalue = s1[0];
for (int i=0; i< 100; i++ ) // for (int i=0; i< vecS1.size(); i++)
....
{
if (s1[i].keyField < minvalue )
{
minvalue =s1[i].keyField;
index = i;
}
}
//----------------------------------------------
However, since there are many such arrays(vectors) with different
struct type
(so, with different "field" name)
How can I define a function (or MACRO?) to get the index
of the minumal item (by comparing the the value of a key field)?
such as MIN(struct_array_variable, field_name)
e.g.
index = MIN(s1, keyField);
to get the index of array "s1" with a minimal value of "keyField".
And ,
index = MIN(s2,f2) get that of "s2" (defined as follows:)
struct s2_t
{
int f2;
// other fields
}
s2_t s2[100]
A similar function is FIND(struct_array, field, value)
to find the index from array "struct_array", where
struct_array[index].field == value;
I think that the sticking point is that how to pass the field name
as a parameter? isn''t it?
Could anyone help me?
Thank you very much!
Jellicle wrote:There are some sturct arrays (or struct vectors), such as:
struct S1_t
{
double keyField ;
..// other fields
}
S1_t s1[100];
std::vector<S1_t> vecS1;
I need to find the index of the item in array "s1" or vector "vecS1"
which
has the minimal value in field "keyField".
Some codes could be:
//----------------------------------------------
double minvalue = s1[0];
You mean
double minvalue = s1[0].keyField;
??
for (int i=0; i< 100; i++ ) // for (int i=0; i< vecS1.size(); i++)
You mean
for (int i=1; i< ...
??
...
{
if (s1[i].keyField < minvalue )
{
minvalue =s1[i].keyField;
index = i;
}
}
//----------------------------------------------
However, since there are many such arrays(vectors) with different
struct type
(so, with different "field" name)
How can I define a function (or MACRO?) to get the index
of the minumal item (by comparing the the value of a key field)?
such as MIN(struct_array_variable, field_name)
e.g.
index = MIN(s1, keyField);
to get the index of array "s1" with a minimal value of "keyField".
And ,
index = MIN(s2,f2) get that of "s2" (defined as follows:)
struct s2_t
{
int f2;
// other fields
}
s2_t s2[100]
A similar function is FIND(struct_array, field, value)
to find the index from array "struct_array", where
struct_array[index].field == value;
I think that the sticking point is that how to pass the field name
as a parameter? isn''t it?
No, it isn''t. The sticking point is to learn about pointers to
members and how they are used.
V
--
Please remove capital ''A''s when replying by e-mail
I do not respond to top-posted replies, please don''t ask
you can get the offset of a field f in a struct s using the following
well-known trick:
#define OFFSET(s,f) &((struct s *) 0)->f
Once you have the offset, it becomes straightforward to solve your problem.
-Shimin
Jellicle wrote:There are some sturct arrays (or struct vectors), such as:
struct S1_t
{
double keyField ;
..// other fields
}
S1_t s1[100];
std::vector<S1_t> vecS1;
I need to find the index of the item in array "s1" or vector "vecS1"
which
has the minimal value in field "keyField".
Some codes could be:
//----------------------------------------------
double minvalue = s1[0];
for (int i=0; i< 100; i++ ) // for (int i=0; i< vecS1.size(); i++)
...
{
if (s1[i].keyField < minvalue )
{
minvalue =s1[i].keyField;
index = i;
}
}
//----------------------------------------------
However, since there are many such arrays(vectors) with different
struct type
(so, with different "field" name)
How can I define a function (or MACRO?) to get the index
of the minumal item (by comparing the the value of a key field)?
such as MIN(struct_array_variable, field_name)
e.g.
index = MIN(s1, keyField);
to get the index of array "s1" with a minimal value of "keyField".
And ,
index = MIN(s2,f2) get that of "s2" (defined as follows:)
struct s2_t
{
int f2;
// other fields
}
s2_t s2[100]
A similar function is FIND(struct_array, field, value)
to find the index from array "struct_array", where
struct_array[index].field == value;
I think that the sticking point is that how to pass the field name
as a parameter? isn''t it?
Could anyone help me?
Thank you very much!
Victor Bazarov wrote:
Jellicle wrote:
Some codes could be:
//----------------------------------------------
double minvalue = s1[0];
You mean
double minvalue = s1[0].keyField;
??for (int i=0; i< 100; i++ ) // for (int i=0; i< vecS1.size(); i++)
You mean
for (int i=1; i< ...
??
You are right exactly :-).
(and I should check if vecS1[0] exists in a vector :-) )
But what I puzzled is that how to handle the various types of
structs and fields in different arrays or vectors.
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