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Internet Message Format  |  1996-08-05  |  2.8 KB
  1. Path: maverick.tad.eds.com!news-admin@tad.eds.com
  2. From: gulleha@vaxixhp3.vaxix.slg.eds.com (Harold Guller)
  3. Newsgroups: comp.lang.c
  4. Subject: Re: simple code, argc, argv, strcmp()
  5. Date: 15 Feb 1996 20:11:11 GMT
  6. Organization: EDS
  7. Message-ID: <4g040v$7jj@maverick.tad.eds.com>
  8. References: <11f7cc$17261a.3b3@daprez> <9602011151.AA04526@dxmint.cern.ch>
  9. Reply-To: gulleha@vaxixhp3.vaxix.sig.eds.com
  10. NNTP-Posting-Host: va057.vaxix.slg.eds.com
  11. X-Newsreader: WinVN 0.91.3
  12.  
  13. In article <9602011151.AA04526@dxmint.cern.ch>, danpop@mail.cern.ch (Dan Pop) says:
  14. >>int main (int argc, char **argv) {
  15. >>
  16. >>  if (!strcmp(argv[1],"-d") || !strcmp(argv[1],"-e")) {
  17. >>    Usage();
  18. >>  }
  19. >...
  20. >>
  21. >>Can someone see what's wrong with this ?
  22. >>am I not using strcmp() right ?
  23. >
  24. >Right :-)
  25. >
  26. >Your code is equivalent to:
  27. >
  28. >    if (strcmp(argv[1],"-d") == 0 || strcmp(argv[1],"-e") == 0) Usage();
  29. >
  30. >Which means that any time the program is correctly invoked, it will call
  31. >Usage!
  32. >
  33. >So:
  34. >
  35. >1. Never use ! with strcmp.  It's a good way to shoot yourself in the foot.
  36.  
  37. You can say that about anything that someone does not understad.
  38. A better solution is to learn the concept.  The "!" operator is widely
  39. used and should be understood.
  40.  
  41.  
  42. >2. Always check what a function is supposed to return before using it.
  43. >   strcmp returns 0 when the strings are equal.
  44.  
  45. >3. Are you sure you didn't mean && when you wrote ||?  Even if !strcmp()
  46. >   would have worked as you thought it did, the || operator would have
  47. >   caused the expression inside the if statement to _always_ evaluate to 1.
  48.  
  49. Why do you advise learning the "&&" and "||" conditions?  These are more
  50. complex than the "!" operator, and he did "shoot himself in the foot".
  51. Shoudn't he use nested if else contrcuts to achieve his purpose?
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