linux code, about array initialization.

[Anonymousgoogledeja]

hi all,

while I read the code from linux sources.

I read the statement

static const struct iw_ioctl_description standard_ioctl[] = {
[SIOCSIWCOMMIT - SIOCIWFIRST] = {
.header_type = IW_HEADER_TYPE_NULL,
},
...
};

I have never read such code. normaly, I will write the code as :

static const struct iw_ioctl_description standard_ioctl[] = {
{
.header_type = IW_HEADER_TYPE_NULL,
},
...
};

anyone would help me? thanks

 

[Keith Thompson]

while I read the code from linux sources.

I read the statement

static const struct iw_ioctl_description standard_ioctl[] = {
[SIOCSIWCOMMIT - SIOCIWFIRST] = {
.header_type = IW_HEADER_TYPE_NULL,
},
...
};

I have never read such code. normaly, I will write the code as :

static const struct iw_ioctl_description standard_ioctl[] = {
{
.header_type = IW_HEADER_TYPE_NULL,
},
...
};

The [SIOCSIWCOMMIT - SIOCIWFIRST] specifies an array index.
Presumably SIOCSIWCOMMIT-SIOCIWFIRST is an integer constant
expression.

By specifying the index values, you don't necessarily have to give the
array elements in order.

 

[Anonymousgoogledeja]

I wonder whether it's gcc specific or ANSI std specific?

while I read the code from linux sources.

I read the statement

static const struct iw_ioctl_description standard_ioctl[] = {
[SIOCSIWCOMMIT - SIOCIWFIRST] = {
.header_type = IW_HEADER_TYPE_NULL,
},
...
};

I have never read such code. normaly, I will write the code as :

static const struct iw_ioctl_description standard_ioctl[] = {
{
.header_type = IW_HEADER_TYPE_NULL,
},
...
};

The [SIOCSIWCOMMIT - SIOCIWFIRST] specifies an array index.
Presumably SIOCSIWCOMMIT-SIOCIWFIRST is an integer constant
expression.

By specifying the index values, you don't necessarily have to give the
array elements in order.

 

[Keith Thompson]

while I read the code from linux sources.

I read the statement

static const struct iw_ioctl_description standard_ioctl[] = {
[SIOCSIWCOMMIT - SIOCIWFIRST] = {
.header_type = IW_HEADER_TYPE_NULL,
},
...
};

I have never read such code. normaly, I will write the code as :

static const struct iw_ioctl_description standard_ioctl[] = {
{
.header_type = IW_HEADER_TYPE_NULL,
},
...
};

The [SIOCSIWCOMMIT - SIOCIWFIRST] specifies an array index.
Presumably SIOCSIWCOMMIT-SIOCIWFIRST is an integer constant
expression.

By specifying the index values, you don't necessarily have to give the
array elements in order.

I wonder whether it's gcc specific or ANSI std specific?

Please don't top-post. Your reply goes below the quoted text, so the
entire article can be read from top to bottom.

Designators in initializers (including both the ".member=value" and
"[index]=value" forms) are a new feature in C99. (The term "ANSI" is
ambiguous; strictly speaking the current 1999 ISO standard is the ANSI
standard, but the term "ANSI" is commonly used to refer to the
1989/1990 ANSI/ISO standard.)

 

[Emmanuel Delahaye]

Anonymousgoogledeja a écrit :

while I read the code from linux sources.

I read the statement

static const struct iw_ioctl_description standard_ioctl[] = {
[SIOCSIWCOMMIT - SIOCIWFIRST] = {
.header_type = IW_HEADER_TYPE_NULL,
},
...
};

I have never read such code. normaly, I will write the code as :

static const struct iw_ioctl_description standard_ioctl[] = {
{
.header_type = IW_HEADER_TYPE_NULL,
},
...
};

anyone would help me? thanks

Read again. 'iw_ioctl_description standard_ioctl' is an *array* of
structure... For an 'absolute' initializing (C99), you also need the index.