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  1. #include <iostream>
  2. #include <stdlib.h>
  3. #include <stdio.h>
  4. #include <string.h>
  5. #include <memory.h>
  6.  
  7. char * replacecstr(char *str, char*substri, char* replacement);
  8.  
  9. /* Here is algorithmic overview.
  10.     1. Copy byte by byte
  11. 	2. If possible substring-start is found, stop copying, note position
  12. 	3. If substring match continues, continue comparing;
  13. 	 3.1 If it fails to match the substring, put us back just after we thought it was a substring
  14. 	 3.2 If the substring is a match, write the replacement instead
  15. 	4. Else, goto 1
  16. 	*/
  17.  
  18. char * replacecstr(char *str, char*substri, char* replacement)
  19. {
  20. 	enum states { searching, possible };
  21.  
  22.     char *substr = substri;
  23. 	char *curptr = str;
  24. 	char *possible_start = str;
  25.  
  26. 	char *first_malloc = (char*)malloc(strlen(str)*10);
  27.  
  28. 	char *writepos = first_malloc;
  29. 	states status = searching;
  30. 	for (;;) {
  31.  
  32.         // **** This part checks if we're at the end of the string, and handles corner-cases
  33. 		if (*curptr == 0) { // End of input string
  34. 			if (status==possible) { // If we thought we might be in a substring...are we?
  35. 			    if (*substr == 0) { // We've matched our substring with our string right at the end, the corner case, so do our replacement
  36. 					char *tmp = replacement;
  37. 					while(*tmp!=0) {
  38. 					    *writepos = *tmp;
  39. 						writepos++;
  40. 						tmp++;
  41. 					}
  42. 				}
  43. 				else { // We thought we were in a substring but we're not, so we need to copy what we missed
  44. 					while (*possible_start) {
  45. 						*writepos = *possible_start;
  46. 						possible_start++;
  47. 						writepos++;
  48. 					}
  49. 				}
  50. 			}
  51. 			break; // We're at the end no matter what, so get out of this loop
  52. 		}
  53.  
  54. 		// **** This part covers what to do when we think we're in a substring
  55. 	    if (status==possible) {
  56. 			if (*substr == 0) // Reached end of substring, found a match!
  57. 			{
  58. 				status = searching;
  59. 				char *tmp = replacement;
  60. 				while(*tmp!=0) {
  61. 				    *writepos = *tmp;
  62. 					writepos++;
  63. 					tmp++;
  64. 				}
  65. 				substr = substri;
  66. 				continue;
  67. 			}
  68. 			else if (*curptr!=*substr) { // Substring doesn't match, time to go back to just after the possible start to see if we have a substring
  69.  
  70. 				status = searching;
  71. 				curptr = possible_start + 1;
  72. 				*writepos = *possible_start;
  73. 				writepos++;
  74. 				substr = substri;
  75. 				continue;
  76. 			}
  77. 			else { // Just another part of the substring
  78. 				curptr++;
  79. 				substr++;
  80. 				continue;
  81. 			}
  82. 		}
  83.  
  84. 		// **** This part checks if we have a possible start to the sub-string
  85. 		if (*curptr==*substr) {
  86. 			status = possible;
  87. 			possible_start = curptr;
  88. 			curptr++;
  89. 			substr++;
  90. 			continue;
  91. 		}
  92.  
  93. 		// **** Thos part continues the byte-by-byte copy
  94. 		*writepos = *curptr;
  95. 		writepos++;
  96. 		curptr++;
  97. 	}
  98.  
  99. 	*writepos = 0;
  100.  
  101. 	int tcpy = strlen(first_malloc)+1;
  102. 	char *malloc2 = (char *)malloc(tcpy);
  103. 	memcpy(malloc2,first_malloc,tcpy);
  104. 	free(first_malloc);
  105. 	return malloc2;
  106. }
  107.  
  108.  
  109. int main()
  110. {
  111. 	char *foo = replacecstr("Hello bob how bbob are you","bob","ann");
  112. 	std::cout << foo;
  113. 	free(foo);
  114.  
  115. 	char foobarre[500];
  116. 	gets(foobarre);
  117. }
Success #stdin #stdout 0.02s 2860KB
comments (?)
stdin 
Standard input is empty
stdout 
Hello ann how bann are you
https://ideone.com/ew5pL
language:
C++ (gcc 8.3)
created:
13 years ago
visibility:
public

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