How to remove special character from string?

Segmentation fault in home-grown C string manipulation code...

• I am working on a string manipulation library in C. I am trying to create my own version of the strchr() function, using the following code: char *es_strchr(char needle, char * haystack) { int count_a = 0; int count_b = 0; int found_needle = 0; char lastchar; char * return_value; for ( ; ; ) { lastchar = haystack[count_a]; if (lastchar == needle) { found_needle = 1; } if (found_needle == 1) { if (lastchar != '\0') { return_value[count_b] = lastchar; count_b++; } } if (lastchar == '\0') { if (found_needle == 1) { return_value[count_b] = lastchar; } break; } count_a++; } return(return_value); } When I try to test this code by creating a test frontend (let's say, test.c), and do the following... char * request = es_strchr(' ', "GET /index.html HTTP/1.0\r\nUser-Agent: EbertSoft-UICI\r\n\r\n ... I get a "segmentation fault" ... but if I remove the space character between "User-Agent:" and "EbertSoft-UICI", the code runs fine. I need to know what's wrong with my es_strchr() function code. Thanks for your help! -- Quinn

• Answer:

  Zefyre, Your code has several problems. One of which is that it does not actually do what strchr() does. We'll get to that in a moment. First, the reason for your crash: You declare a char pointer called return_value. A pointer has to point at something. You don't initialize it, and you don't point it at anything valid. Therefore, it is very likely to crash if you try to use it. Note that you crash when your code succeeds in matching needle. This condition allows your code to run the part where you try to set return_value[count_b]. Since this location is a pointer off into la-la land, you crash. To use a char pointer this way, you need to allocate some memory for it to point at. For example, malloc(). However, all of this is actually irrelevant. You don't need any of this to duplicate strchr. To work like strchr, your code needs to return a pointer into haystack. The way your code is currently written, even if you fix the crash, you will simply return the character you were originally looking for. The point of strchr is to return a pointer that show where in the original string the character appears. MSDN Library Reference for strchr http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vclib/html/_crt_strchr.2c_.wcschr.2c_._mbschr.asp Here is a commented implementation of strchr: char *my_strchr(char needle, char *haystack) { // Declare some char pointers char *return_value; char *cp; // Initialize return value return_value = NULL; // Make sure haystack is valid if(haystack != NULL) { // Set pointer to beginning of haystack cp = haystack; // Run until we either find a match or // get to the end of haystack. while((*cp != '\0') && (return_value == NULL)) { // If we found a match, set return value // and exit the loop if(*cp == needle) return_value = cp; // Advance cp cp++; } } // If we didn't find a match, return_value is // still NULL. Otherwise, it is pointing at the // first matching character in haystack. return(return_value); } In your example above, return_value would be " EbertSoft-UICI". I hope this clarifies things for you. Please let me know if you need any of the techniques in the example explained. Search strategy: None. I've just done this before! - Hammer