Side-Effectful Expressions in C (2023)

6 comments

• amavect 2 hours ago

  For fun, my attempt to rewrite the functions. Eliminate ++ and pointer arithmetic by introducing a counter. Obviously less terse.

    void *my_memcpy(void *dst, const void *src, size_t n)
    {
     const uint8_t *s = src;
     uint8_t *d = dst;
     for (size_t i = 0; i < n; i += 1) d[i] = s[i];
     return dst;
    }
  
    int powi(int x, int y)
    {
     int result = 1;
     for (int i = 0; i < y; i += 1) result *= x;
     return result;
    }
  

  For itoa, I experiment with the comma operator to show the post-increment on the same line, but visibly after. I also move the negation sign block to the absolute value block.

    void itoa(int n, char s[])
    {
     int i = 0;
     if (n < 0){
      n = -n;
      s[0] = '-', s += 1; // exclude from reverse
     }
     do{
      s[i] = n % 10 + '0', i += 1;
      n /= 10;
     }while(n > 0);
     s[i] = '\0';
     // reverse
     for(int j = 0, hi = i / 2; j < hi; j += 1) {
      i -= 1;
      char swap = s[j];
      s[j] = s[i];
      s[i] = swap;
     }
    }
  

  Test code:

    #include <stdio.h>
    #include <stdint.h>
    // insert functions
    int main(void){
     char src[] = "hello";
     char dst[10];
     my_memcpy(dst, src, sizeof(src));
     printf("%s == hello\n", dst);
     printf("%d == 27\n", powi(3,3));
     itoa(-12345, dst);
     printf("%s == -12345\n", dst);
     itoa(0, dst);
     printf("%s == 0\n", dst);
    }

• commandlinefan 4 hours ago

  Maybe I'm just Stockholm syndrome-d into the C programming language, but none of the examples here are terribly compelling to me - I love articles about C's weirdness, but I don't really think his before and after comparisons make a case for a replacement for C.

  [-]
  • up2isomorphism 4 hours ago

    Yeah, just because you can grab from your refrigerator a piece of raw meat and put it in a cup of milk in 10 secs and it tastes bad doesn’t mean the refrigerator should be blamed because of this.

    [-]
    • volemo 2 hours ago

      Yeah, but if the refrigerator is built in a way that makes it very easy to grab some refrigerant when you want to pour yourself a glass of milk (to the point that one has to be careful and skilled to safely drink milk), maybe we should get a new refrigerator.

• andrewla 6 hours ago

  Really this is mainly about the ++ and -- operators. I think Go made the right call here and allows these only as statements, not as expressions. I will basically never use these in code I write and will remove it from code I maintain or review; the only value add is compactness which is very rarely a goal.

  The other side effect expression here is the equals operator; once again, this should not be an expression but should just be a statement. Once again this is used (intentionally) mainly for compactness and unintentionally used to create messy bugs. I do find the "yoda" style checks to be aesthetically unpleasing so I'm party of the problem here.

  Maybe it's time to add `-Wno-crement-expressions` and `-Wno-assignment-expressions`. `-Wparentheses` gets you part of the way to the second but even the legitimate uses are ugly to my eye.

  [-]
  • HackerThemAll 2 hours ago

    > Maybe it's time to add `-Wno-crement-expressions` and `-Wno-assignment-expressions`. `-Wparentheses`

    Aren't there static analyzers in widespread use that would catch these?