3 ms·

What are the good alternatives? You can either copy memory manually, or have a system like C++'s that causes lots of tiny allocations, which is very inefficient

What are the good alternatives? You can either copy memory manually, or have a system like C++'s that causes lots of tiny allocations, which is very inefficient. Both in space and time. You can also opt for immutable strings to be able to share strings more conveniently and efficiently, at the cost of O(n^2) build time (where automatic optimizations fail) or decreased convenience (explicit string-stream aka string builder). If efficiency is not a concern for you and you rather like the convenience, good for you. Personally I feel plain const char pointers (plus length, depending on expected size) are good enough to emulate the immutable string type. For modifiable strings, I still prefer viewing them as chunks of memory, using char pointer + length + capacity. Nice thing is, you can easily go from the former to the latter in the lifetime of any one string. You can also pool many strings in large chunks if you build only one string at any one time.

adrianN 8y ago
Whatever alternative reliably prevents buffer overflows, so pretty much anything but char*.
pjmlp 8y ago
You care about that after a profiler proves that it is actually a problem to the expected delivery SLAs for the application. Micro-optimizing each line of C code based on gut feeling is not an option if quality matters.
- jstimpfle 8y ago
  It's not about the code, but about choice of data structure. Unfortunately that has to be planned ahead to some degree. You can't really optimize it after the fact. Typically a choice affects more than a single line of code, but that doesn't mean "microoptimizing every line of code", which is obviously a bad idea.
  - pjmlp 8y ago
    Sure you can, that is what Abstract Data Types architecture design is all about. Naturally, when one creates struts and accesses the fields directly there is no way out of a bad design.
    - jstimpfle 8y ago
      That's a pipe dream. There are a handful of successful abstractions, like streams or associative containers, or strings for that matter. Even those quickly get too abstract for serious use, and you need to actually expose what's really happening to make sensible choices, because there are vastly different kinds of streams or containers (or even strings), because, well, those are abstractions. Other more far reaching design choices could be: when and how much precomputation is done, data loading strategies, data-flow oriented vs control flow oriented, threading strategies, etc. You can't hide these choices behind a name. They deeply affect the structure of the program.
      - pjmlp 8y ago
        A pipe dream delivered into production around 2000, for a distributed CRM platform running across Aix, Solaris, HP-UX, Red-Hat Linux, Windows NT/2000.
- gnulinux 8y ago
  This is a horrible stance and this is repeated like broken record. Please stop saying this? A good software engineer should know (1) a suitable data structure to solve the problem in hand (2) algorithms that have certain asymptotic characteristic that makes most sense for the problem (what assumptions can you make). "Premature optimization is the root of all evil" can be used for and only for "optimization". Choosing the right data structure is never an optimization, it's a design choice. You can't just start coding everything with a linked list and then optimize bottlenecks, that's just not how it works.
  - pjmlp 8y ago
    As you say "A good software engineer should know a suitable data structure to solve the problem in hand". So I expect a good software engineer on my team to be able to design a data structure where the fact that a linked list is being used doesn't hinder to change it afterwards to an array, a B-Tree or what have you. Without changing a single line of client code I might add. Such good software engineer will certainly had attended an algorithms and data structures class on their CS degree and be aware of architecture designs based on Abstract Data Types. Yes, even in C with its flaky translation units instead of proper module systems, it is possible to implement Abstract Data Types application architectures, which any good software engineer can easily tackle. And for those that aspire to reach that level, here are a few examples. "Algorithms + Data Structures = Programs" by Niklaus Wirth, 1st edition is Modula-2, the 2nd in Oberon "Introduction to Algorithms" by Thomas Cormen, Clifford Stein, Ronald Rivest, Charles Leiserson "Abstract data types and Modula-2: a worked example of design using data abstraction" by Richard Mitchell "Abstract Data Types in Modula-2" by Rachel Harrison "Abstract Data Types and Algorithms" by Azmoodeh, Manoochchr
    - gnulinux 8y ago
      Your comment still doesn't make sense, even though you decided to choose a certain ADS and then latee decide on the implementation later based on empirical performance data, this is still not unusual. For (1) this is not how people write C. There are ADS libraries in C with which you wouldn't need need to use any DS that you can't change but this is not a usual way to write C code. This will also come with the overhead of pointer indirection and worse cache performance since all your objects will be void* stored in the DS (unless you m4 or macro generate your DS with all datatypes. This is what linux does for example, and I sometimes use this technique too, but this hardly the usual way to write C code). And (2) usually complex problems require special enough datastructures that it doesn't make much sense talk about ADSs. Everyone can code basic foobar with List interface then decide to use ArrayList or LinkedList based on performance. It's more interesting when the programmer decides to use a set, a hash map, a bloom filter etc to solve the problem as any other type wouldn't make sense.

adrianN 8y ago

Whatever alternative reliably prevents buffer overflows, so pretty much anything but char*.

pjmlp 8y ago

You care about that after a profiler proves that it is actually a problem to the expected delivery SLAs for the application. Micro-optimizing each line of C code based on gut feeling is not an option if quality matters.

jstimpfle 8y ago
It's not about the code, but about choice of data structure. Unfortunately that has to be planned ahead to some degree. You can't really optimize it after the fact. Typically a choice affects more than a single line of code, but that doesn't mean "microoptimizing every line of code", which is obviously a bad idea.
- pjmlp 8y ago
  Sure you can, that is what Abstract Data Types architecture design is all about. Naturally, when one creates struts and accesses the fields directly there is no way out of a bad design.
  - jstimpfle 8y ago
    That's a pipe dream. There are a handful of successful abstractions, like streams or associative containers, or strings for that matter. Even those quickly get too abstract for serious use, and you need to actually expose what's really happening to make sensible choices, because there are vastly different kinds of streams or containers (or even strings), because, well, those are abstractions. Other more far reaching design choices could be: when and how much precomputation is done, data loading strategies, data-flow oriented vs control flow oriented, threading strategies, etc. You can't hide these choices behind a name. They deeply affect the structure of the program.
    - pjmlp 8y ago
      A pipe dream delivered into production around 2000, for a distributed CRM platform running across Aix, Solaris, HP-UX, Red-Hat Linux, Windows NT/2000.
gnulinux 8y ago
This is a horrible stance and this is repeated like broken record. Please stop saying this? A good software engineer should know (1) a suitable data structure to solve the problem in hand (2) algorithms that have certain asymptotic characteristic that makes most sense for the problem (what assumptions can you make). "Premature optimization is the root of all evil" can be used for and only for "optimization". Choosing the right data structure is never an optimization, it's a design choice. You can't just start coding everything with a linked list and then optimize bottlenecks, that's just not how it works.
- pjmlp 8y ago
  As you say "A good software engineer should know a suitable data structure to solve the problem in hand". So I expect a good software engineer on my team to be able to design a data structure where the fact that a linked list is being used doesn't hinder to change it afterwards to an array, a B-Tree or what have you. Without changing a single line of client code I might add. Such good software engineer will certainly had attended an algorithms and data structures class on their CS degree and be aware of architecture designs based on Abstract Data Types. Yes, even in C with its flaky translation units instead of proper module systems, it is possible to implement Abstract Data Types application architectures, which any good software engineer can easily tackle. And for those that aspire to reach that level, here are a few examples. "Algorithms + Data Structures = Programs" by Niklaus Wirth, 1st edition is Modula-2, the 2nd in Oberon "Introduction to Algorithms" by Thomas Cormen, Clifford Stein, Ronald Rivest, Charles Leiserson "Abstract data types and Modula-2: a worked example of design using data abstraction" by Richard Mitchell "Abstract Data Types in Modula-2" by Rachel Harrison "Abstract Data Types and Algorithms" by Azmoodeh, Manoochchr
  - gnulinux 8y ago
    Your comment still doesn't make sense, even though you decided to choose a certain ADS and then latee decide on the implementation later based on empirical performance data, this is still not unusual. For (1) this is not how people write C. There are ADS libraries in C with which you wouldn't need need to use any DS that you can't change but this is not a usual way to write C code. This will also come with the overhead of pointer indirection and worse cache performance since all your objects will be void* stored in the DS (unless you m4 or macro generate your DS with all datatypes. This is what linux does for example, and I sometimes use this technique too, but this hardly the usual way to write C code). And (2) usually complex problems require special enough datastructures that it doesn't make much sense talk about ADSs. Everyone can code basic foobar with List interface then decide to use ArrayList or LinkedList based on performance. It's more interesting when the programmer decides to use a set, a hash map, a bloom filter etc to solve the problem as any other type wouldn't make sense.