c - Unhandled exception at 0x0f6cf9c4 in server.exe: 0xC0000005: Access violation reading location 0x00000001 -

here code have written in visual studio 2008. data in receive array & using data, preparing response it. error "unhandled exception @ 0x0f6cf9c4 in server.exe: 0xc0000005: access violation reading location 0x00000001." every time @ "strcat" function when code runs.

    byte receive[50];     unsigned char result[50];      int index = 0;     char *type;     char *s =  "ff ff ff 1d 00 01 01 0b 00 01";     char *s1 = "03 00 98 ac 06 36 6f 92";     int i;   if (receive[i] == 0x18)     {          if ((receive[i+1] == 0x20) || (receive[i+1] == 0x21) || (receive[i+1] == 0x22) || (receive[i+1] == 0x23) || (receive[i+1] == 0x24) || (receive[i+1] == 0x25))         {              if (receive[i+2] == 0x00)             {                 result[index] = receive[i-4];`enter code here`                 result[index+1] = receive[i-3];                 index = index+2;                 type = "report";             }         }     } }  index = 0;  if (type == "report") {         strcat(s, result[index]);         strcat(s, result[index+1]);         strcat(s, s1);         strcat(s, array1[j]);         strcat(s, array1[j+1]);         strcat(s, array1[j+2]);         strcat(s, array1[j+3]);         strcat(s, array1[j+4]); 

a candidate cause of crashes though, try modify string literals.

when strcat(s, ...) modify string literal s points to. string literal read-only fixed-size array of characters terminated special character '\0'. when use such string literal destination in strcat call first of modify read-only array, , write out of bounds of array. both of these things leads undefined behavior.

you need create own array, big enough fit data want write it. , don't forget space string terminator.

furthermore use e.g. result[index] string. elements in result single characters, not pointers strings. need use strncat concatenate single characters. and need pass pointer character. depending on array1 might have similar problems.

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as possible solution might want use sprintf instead of series of invalid strcat calls:

sprintf(dest, "%s%c%c%s%c%c%c%c%c",         s,         result[index],         result[index+1],         s1,         array1[j],         array1[j+1],         array1[j+2],         array1[j+3],         array1[j+4]);