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getsockopt api design questions
Improve INSERT-per-second performance of SQLite?Understanding functions and pointers in CWhat is the difference between writing to a file and a mapped memory?Can I get a pointer to a struct as a parameter from a function in C?What is Linux’s native GUI API?C - Which is the advantage for the user of const in parameters of functions that are not pointers?What is the intention/benefit of malloc returning type void *?Setting custom value to void pointer in gmockWhy the char has to be a pointer instead of a type of char?Define a C API with callbacks
we can see the api is defined as blow
int getsockopt(int sockfd, int level, int optname,
void *optval, socklen_t *optlen);
Question 1:
Suppose given a level and optname, then we know the optlen, why do we need the user to provide the optlen parameter as well?
even user provide the optlen, why it is a pointer to socklen_t rather than socklen_t directly? do the implementation will change the value of optlen somehow?
Thanks
c linux getsockopt
asked Mar 8 at 2:11
zhihuifanzhihuifan
3651214
add a comment |
we can see the api is defined as blow
int getsockopt(int sockfd, int level, int optname,
void *optval, socklen_t *optlen);
Question 1:
Suppose given a level and optname, then we know the optlen, why do we need the user to provide the optlen parameter as well?
even user provide the optlen, why it is a pointer to socklen_t rather than socklen_t directly? do the implementation will change the value of optlen somehow?
Thanks
c linux getsockopt
asked Mar 8 at 2:11
zhihuifanzhihuifan
3651214
add a comment |
we can see the api is defined as blow
int getsockopt(int sockfd, int level, int optname,
void *optval, socklen_t *optlen);
Question 1:
Suppose given a level and optname, then we know the optlen, why do we need the user to provide the optlen parameter as well?
even user provide the optlen, why it is a pointer to socklen_t rather than socklen_t directly? do the implementation will change the value of optlen somehow?
Thanks
c linux getsockopt
asked Mar 8 at 2:11
zhihuifanzhihuifan
3651214
we can see the api is defined as blow
int getsockopt(int sockfd, int level, int optname,
void *optval, socklen_t *optlen);
Question 1:
Suppose given a level and optname, then we know the optlen, why do we need the user to provide the optlen parameter as well?
even user provide the optlen, why it is a pointer to socklen_t rather than socklen_t directly? do the implementation will change the value of optlen somehow?
Thanks
c linux getsockopt
c linux getsockopt
asked Mar 8 at 2:11
zhihuifanzhihuifan
3651214
asked Mar 8 at 2:11
zhihuifanzhihuifan
3651214
asked Mar 8 at 2:11
zhihuifanzhihuifan
3651214
asked Mar 8 at 2:11
zhihuifanzhihuifan
3651214
asked Mar 8 at 2:11
zhihuifanzhihuifan
3651214
3651214
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
Have you looked at the Linux man page for getsockopt(2) or the POSIX specification of getsockopt()?
The
optlenparameter is an in-out parameter. On input, it specifies how much space is available in theoptvalspace, and on output, it reports how much of the space inoptvalwas written to.Yes, the implementation changes the value of
*optlen.
For example, POSIX says:
If the size of the option value is greater than option_len, the value stored in the object pointed to by the option_value argument shall be silently truncated. Otherwise, the object pointed to by the option_len argument shall be modified to indicate the actual length of the value.
The specification uses option_len where you used optlen, and option_value where you used optval.
answered Mar 8 at 7:46
Jonathan LefflerJonathan Leffler
572k936861038
add a comment |
It is easy to understand.Because api faces many options and needs to prepare for future options.
Example:
assume "optname=1" , it will return 64bytes strings. At this time ,you need :
char optval[64];
socklen_t optlen=64;
answered Mar 8 at 6:28
Y.JieY.Jie
114
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
Have you looked at the Linux man page for getsockopt(2) or the POSIX specification of getsockopt()?
The
optlenparameter is an in-out parameter. On input, it specifies how much space is available in theoptvalspace, and on output, it reports how much of the space inoptvalwas written to.Yes, the implementation changes the value of
*optlen.
For example, POSIX says:
If the size of the option value is greater than option_len, the value stored in the object pointed to by the option_value argument shall be silently truncated. Otherwise, the object pointed to by the option_len argument shall be modified to indicate the actual length of the value.
The specification uses option_len where you used optlen, and option_value where you used optval.
answered Mar 8 at 7:46
Jonathan LefflerJonathan Leffler
572k936861038
add a comment |
Have you looked at the Linux man page for getsockopt(2) or the POSIX specification of getsockopt()?
The
optlenparameter is an in-out parameter. On input, it specifies how much space is available in theoptvalspace, and on output, it reports how much of the space inoptvalwas written to.Yes, the implementation changes the value of
*optlen.
For example, POSIX says:
If the size of the option value is greater than option_len, the value stored in the object pointed to by the option_value argument shall be silently truncated. Otherwise, the object pointed to by the option_len argument shall be modified to indicate the actual length of the value.
The specification uses option_len where you used optlen, and option_value where you used optval.
answered Mar 8 at 7:46
Jonathan LefflerJonathan Leffler
572k936861038
add a comment |
Have you looked at the Linux man page for getsockopt(2) or the POSIX specification of getsockopt()?
The
optlenparameter is an in-out parameter. On input, it specifies how much space is available in theoptvalspace, and on output, it reports how much of the space inoptvalwas written to.Yes, the implementation changes the value of
*optlen.
For example, POSIX says:
If the size of the option value is greater than option_len, the value stored in the object pointed to by the option_value argument shall be silently truncated. Otherwise, the object pointed to by the option_len argument shall be modified to indicate the actual length of the value.
The specification uses option_len where you used optlen, and option_value where you used optval.
answered Mar 8 at 7:46
Jonathan LefflerJonathan Leffler
572k936861038
Have you looked at the Linux man page for getsockopt(2) or the POSIX specification of getsockopt()?
The
optlenparameter is an in-out parameter. On input, it specifies how much space is available in theoptvalspace, and on output, it reports how much of the space inoptvalwas written to.Yes, the implementation changes the value of
*optlen.
For example, POSIX says:
If the size of the option value is greater than option_len, the value stored in the object pointed to by the option_value argument shall be silently truncated. Otherwise, the object pointed to by the option_len argument shall be modified to indicate the actual length of the value.
The specification uses option_len where you used optlen, and option_value where you used optval.
answered Mar 8 at 7:46
Jonathan LefflerJonathan Leffler
572k936861038
answered Mar 8 at 7:46
Jonathan LefflerJonathan Leffler
572k936861038
answered Mar 8 at 7:46
Jonathan LefflerJonathan Leffler
572k936861038
answered Mar 8 at 7:46
Jonathan LefflerJonathan Leffler
572k936861038
572k936861038
add a comment |
add a comment |
It is easy to understand.Because api faces many options and needs to prepare for future options.
Example:
assume "optname=1" , it will return 64bytes strings. At this time ,you need :
char optval[64];
socklen_t optlen=64;
answered Mar 8 at 6:28
Y.JieY.Jie
114
add a comment |
It is easy to understand.Because api faces many options and needs to prepare for future options.
Example:
assume "optname=1" , it will return 64bytes strings. At this time ,you need :
char optval[64];
socklen_t optlen=64;
answered Mar 8 at 6:28
Y.JieY.Jie
114
add a comment |
It is easy to understand.Because api faces many options and needs to prepare for future options.
Example:
assume "optname=1" , it will return 64bytes strings. At this time ,you need :
char optval[64];
socklen_t optlen=64;
answered Mar 8 at 6:28
Y.JieY.Jie
114
It is easy to understand.Because api faces many options and needs to prepare for future options.
Example:
assume "optname=1" , it will return 64bytes strings. At this time ,you need :
char optval[64];
socklen_t optlen=64;
answered Mar 8 at 6:28
Y.JieY.Jie
114
answered Mar 8 at 6:28
Y.JieY.Jie
114
answered Mar 8 at 6:28
Y.JieY.Jie
114
answered Mar 8 at 6:28
Y.JieY.Jie
114
114
add a comment |
add a comment |
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