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  1. #include <stdio.h>
  2.  
  3. struct timeval
  4. {
  5.   long tv_sec;
  6.   long tv_usec;
  7. };
  8.  
  9. int timeval_subtract(struct timeval *result, struct timeval *x, struct timeval *y)
  10. {  
  11.   // preserve *y
  12.   struct timeval yy = *y;
  13.   y = &yy;
  14.  
  15.   /* Perform the carry for the later subtraction by updating y. */  
  16.   if (x->tv_usec < y->tv_usec) {  
  17.     int nsec = (y->tv_usec - x->tv_usec) / 1000000 + 1;  
  18.     y->tv_usec -= 1000000 * nsec;  
  19.     y->tv_sec += nsec;  
  20.   }  
  21.   if (x->tv_usec - y->tv_usec > 1000000) {  
  22.     int nsec = (y->tv_usec - x->tv_usec) / 1000000;  
  23.     y->tv_usec += 1000000 * nsec;  
  24.     y->tv_sec -= nsec;  
  25.   }  
  26.  
  27.   /* Compute the time remaining to wait.
  28.      tv_usec is certainly positive. */  
  29.   result->tv_sec = x->tv_sec - y->tv_sec;  
  30.   result->tv_usec = x->tv_usec - y->tv_usec;  
  31.  
  32.   /* Return 1 if result is negative. */  
  33.   return x->tv_sec < y->tv_sec;  
  34. }
  35.  
  36. struct timeval testData00 = { 0, 0 };
  37. struct timeval testData01 = { 0, 1 };
  38. struct timeval testData01000000 = { 0, 1000000 };
  39. struct timeval testData01000001 = { 0, 1000001 };
  40.  
  41. int main(void)
  42. {
  43.   struct timeval diff;
  44.   int res;
  45.  
  46.   res = timeval_subtract(&diff, &testData00, &testData00);
  47.   printf("%d %ld:%ld\n", res, diff.tv_sec, diff.tv_usec);
  48.  
  49.   res = timeval_subtract(&diff, &testData01, &testData01);
  50.   printf("%d %ld:%ld\n", res, diff.tv_sec, diff.tv_usec);
  51.  
  52.   res = timeval_subtract(&diff, &testData01, &testData00);
  53.   printf("%d %ld:%ld\n", res, diff.tv_sec, diff.tv_usec);
  54.  
  55.   res = timeval_subtract(&diff, &testData00, &testData01);
  56.   printf("%d %ld:%ld\n", res, diff.tv_sec, diff.tv_usec);
  57.  
  58.   res = timeval_subtract(&diff, &testData01000000, &testData00);
  59.   printf("%d %ld:%ld\n", res, diff.tv_sec, diff.tv_usec);
  60.  
  61.   res = timeval_subtract(&diff, &testData01000001, &testData00);
  62.   printf("%d %ld:%ld\n", res, diff.tv_sec, diff.tv_usec);
  63.  
  64.   return 0;
  65. }
  66.  
Success #stdin #stdout 0s 1832KB
comments (?)
stdin
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Standard input is empty
stdout
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0 0:0
0 0:0
0 0:1
1 -1:999999
0 0:1000000
1 -1:2000001
https://ideone.com/WJDfAk
language:
C99 (gcc 8.3)
created:
11 years ago
visibility:
public

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