4 ms·

Do we have a source for what the intended purpose is? I think you speak well to the effective purpose, but I'm not sure if it was that clear when it was introdu

Do we have a source for what the intended purpose is? I think you speak well to the effective purpose, but I'm not sure if it was that clear when it was introduced.

lemmiwinks 4y ago
https://devblogs.microsoft.com/oldnewthing/20050107-00/?p=36773 https://devblogs.microsoft.com/oldnewthing/20050107-00/?p=36...
- kzrdude 4y ago
  Doesn't say anything about the intention as understood when it was introduced
masklinn 4y ago
> I think you speak well to the effective purpose, but I'm not sure if it was that clear when it was introduced. It was completely clear, and can easily be inferred from its specified behaviour. It's just completely useless nowadays, because its purpose is essentially obsolete, because the data type it works with is almost never used anymore. strncpy works with fixed-size nul-padded fields as you'd find in e.g. mainframe-type software. That is why it: - fills the destination buffer with NULs if the source is shorter - does not nul-terminate if the source is the same size or longer than the destination strncpy is essentially equivalent to zero-ing a buffer of size `n` then copying the first `n` bytes of src (up to the first nul) in the target
- kzrdude 4y ago
  That's your understanding now. Fine, but not evidence of what someone else thought about this some decades ago. (I don't use strncpy and don't defend its functionality, just want to know what was intended when it was introduced.)
  - kzrdude 4y ago
    I found an actual quote of a source which verifies the intention for fixed-length fields: https://softwareengineering.stackexchange.com/a/438090 https://softwareengineering.stackexchange.com/a/438090
  - spc476 4y ago
    On early Unix systems, the directory structure was a simple 16-byte record; 14 bytes for the name, and 2 bytes for the inode. [1] strncpy() was used to simply record the file name into this structure. [1] "UNIX Implementation" by Ken Thompson, _The Bell System Technical Journal_, July-August 1978, Vol 57, No 6, Part 2, pg 1942.
- tjoff 4y ago
  Many protocols still relevant today make use of that structure, it still has widespread use.
  - masklinn 4y ago
    For the average protocol you're going to init the entire message then set into it, you don't need to fully zero fields. This is mostly relevant to write into existing memory or memory-mapped records.
    - tjoff 4y ago
      Sometimes yes, but you must also not null-terminate the strings in those cases. And on embedded devices you are often memory constrained so you might reuse an existing structure.

Do we have a source for what the intended purpose is? I think you speak well to the effective purpose, but I'm not sure if it was that clear when it was introduced.

lemmiwinks 4y ago

https://devblogs.microsoft.com/oldnewthing/20050107-00/?p=36773 https://devblogs.microsoft.com/oldnewthing/20050107-00/?p=36...

kzrdude 4y ago
Doesn't say anything about the intention as understood when it was introduced

masklinn 4y ago

> I think you speak well to the effective purpose, but I'm not sure if it was that clear when it was introduced. It was completely clear, and can easily be inferred from its specified behaviour. It's just completely useless nowadays, because its purpose is essentially obsolete, because the data type it works with is almost never used anymore. strncpy works with fixed-size nul-padded fields as you'd find in e.g. mainframe-type software. That is why it: - fills the destination buffer with NULs if the source is shorter - does not nul-terminate if the source is the same size or longer than the destination strncpy is essentially equivalent to zero-ing a buffer of size `n` then copying the first `n` bytes of src (up to the first nul) in the target

kzrdude 4y ago
That's your understanding now. Fine, but not evidence of what someone else thought about this some decades ago. (I don't use strncpy and don't defend its functionality, just want to know what was intended when it was introduced.)
- kzrdude 4y ago
  I found an actual quote of a source which verifies the intention for fixed-length fields: https://softwareengineering.stackexchange.com/a/438090 https://softwareengineering.stackexchange.com/a/438090
- spc476 4y ago
  On early Unix systems, the directory structure was a simple 16-byte record; 14 bytes for the name, and 2 bytes for the inode. [1] strncpy() was used to simply record the file name into this structure. [1] "UNIX Implementation" by Ken Thompson, _The Bell System Technical Journal_, July-August 1978, Vol 57, No 6, Part 2, pg 1942.
tjoff 4y ago
Many protocols still relevant today make use of that structure, it still has widespread use.
- masklinn 4y ago
  For the average protocol you're going to init the entire message then set into it, you don't need to fully zero fields. This is mostly relevant to write into existing memory or memory-mapped records.
  - tjoff 4y ago
    Sometimes yes, but you must also not null-terminate the strings in those cases. And on embedded devices you are often memory constrained so you might reuse an existing structure.