atoi and INFINITY

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  • migurus
    #1

    atoi and INFINITY

    I see that atof and strtod both recognize "INF", or "+INF", or "-INF"
    as special case and return accordingly infinite value. But atoi and
    strtol do not know about this special case - why? Is there a trick to
    it?

    example to demonstrate this feature:
    #include <stdio.h>
    #include <stdlib.h>
    #include <errno.h>
    #include <limits.h>
    main(int argc, char *argv[])
    {
    long lx;
    double dx;
    char buf[20], *p = NULL;

    strcpy(buf, argc == 2 ? argv[1] : "+INF");

    lx = atol(buf); printf("lx=%li\ n", lx);
    dx = atof(buf); printf("dx=%f\n ", dx);

    lx = strtol(buf, &p, 10);
    printf("lx=%li, p=%s, errno=%i\n", lx, p, errno);

    dx = strtod(buf, &p);
    printf("dx=%f, p=%s, errno=%i\n", dx, p, errno);
    exit(0);
    }

    Please see results below

    Compiled under SCO OSR5 (tried both native SCO compiler and gcc)

    ../c '+INF'
    lx=0
    dx=inf
    lx=0, p=INF, errno=22
    dx=inf, p=, errno=22

    ../c '-INF'
    lx=0
    dx=-inf
    lx=0, p=-INF, errno=22
    dx=-inf, p=, errno=22


    Very similar behavoir under linux and gcc (errno works differently
    somehow):
    ../c '+INF'
    lx=0
    dx=inf
    lx=0, p=+INF, errno=0
    dx=inf, p=, errno=0

    ../c '-INF'
    lx=0
    dx=-inf
    lx=0, p=-INF, errno=0
    dx=-inf, p=, errno=0

    Any thoughts whether this is a problem with atoi/strtol? I expected
    them behave similarly to atof/strtod, maybe my expectations are
    unwarranted?
    Tags: None
    • Owen Jacobson
      #2
      Re: atoi and INFINITY

      On Apr 15, 5:00 pm, migurus <migu...@gmail. comwrote:
      I see that atof and strtod both recognize "INF", or "+INF", or "-INF"
      as special case and return accordingly infinite value. But atoi and
      strtol do not know about this special case - why? Is there a trick to
      it?
      >
      example to demonstrate this feature:
      #include <stdio.h>
      #include <stdlib.h>
      #include <errno.h>
      #include <limits.h>
      main(int argc, char *argv[])
      {
        long  lx;
        double dx;
        char  buf[20], *p = NULL;
      >
              strcpy(buf, argc == 2 ? argv[1] : "+INF");
      >
              lx = atol(buf); printf("lx=%li\ n", lx);
              dx = atof(buf); printf("dx=%f\n ", dx);
      >
              lx = strtol(buf, &p, 10);
              printf("lx=%li, p=%s, errno=%i\n", lx, p, errno);
      >
              dx = strtod(buf, &p);
              printf("dx=%f, p=%s, errno=%i\n", dx, p, errno);
              exit(0);
      >
      }
      >
      Please see results below
      >
      Compiled under SCO OSR5 (tried both native SCO compiler and gcc)
      >
      ./c '+INF'
      lx=0
      dx=inf
      lx=0, p=INF, errno=22
      dx=inf, p=, errno=22
      >
      ./c '-INF'
      lx=0
      dx=-inf
      lx=0, p=-INF, errno=22
      dx=-inf, p=, errno=22
      >
      Very similar behavoir under linux and gcc (errno works differently
      somehow):
      ./c '+INF'
      lx=0
      dx=inf
      lx=0, p=+INF, errno=0
      dx=inf, p=, errno=0
      >
      ./c '-INF'
      lx=0
      dx=-inf
      lx=0, p=-INF, errno=0
      dx=-inf, p=, errno=0
      >
      Any thoughts whether this is a problem with atoi/strtol? I expected
      them behave similarly to atof/strtod, maybe my expectations are
      unwarranted?
      Even on systems where floating-point values have representable
      infinities, integral types do not have infinities. There would be no
      value to correctly represent the result of atol("INF").

      -o

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