String parsing in C. Copying a part of a string to another string -

i'm trying write function convert escape sequences in string in non-printable form. if have string "this \n makes new line", "this makes new line". far i've got this. i'm calling main:

int main() {     unescape("this \\n\\n \\t\\t\\t string number \\t 7.");     return 0; }  char* unescape(char* s) {     char *esc[2] = {"\\n", "\\t"};     int i;     char* uus = (char*)calloc(80, sizeof(char));     char* uus2 = (char*)calloc(80,sizeof(char));      strncpy(uus, s, strlen(s));      for(i = 0; < 2; i++)     {         while(strstr(uus, esc[i]) != null) //checks if \\n can found         {             //printf("\n\n%p\n\n", strstr(uus, esc[i]));             int c = strstr(uus, esc[i]) - uus; //gets difference between address of beginning of string , location                                            //where searchable string found             uus2 = strncpy(uus2, uus, c); //copies beginning of string new string              //add check esc being used             strcat(uus2, "\n"); //adds non-printable form of escape sequence             printf("%s", uus2);              //should clear string uus before writing uus2              strncpy(uus, uus2, strlen(uus2)); //copies string uus2 uus can checked again         }     }     //this should return in end.  } 

basically, need now, take part string uus after "\n" , add string uus2 can run while loop again. thought using strtok hit wall makes 2 separate strings using kind of delimiter not there in case.

edit: adding rest of string uus2 should before strncpy. code without it.

edit vol2: code works , ended using. edited ruud's version bit function had use had return string. lot.

char* unescape(char* s) {     char *uus = (char*) calloc(80, sizeof(char));     int = 0;      while (*s != '\0')     {         char c = *s++;             if (c == '\\' && *s != '\0')             {                 c = *s++;                 switch (c)                 {                 case 'n': c = '\n'; break;                 case 't': c = '\t'; break;                 }             }         uus[i] = c;         i++;     }     uus[i] = '\0';     return uus; } 

i agree anonymouse. both clumsy , inefficient replace first \n, \t. instead, make single pass through string, replacing escape characters go.

i left space allocation out in code sample below; imho separate responsibility, not part of algorithm, , such not belong in same function.

void unescape(char *target, const char *source) {     while (*source != '\0')     {         char c = *source++;         if (c == '\\' && *source != '\0')         {             c = *source++;             switch (c)             {                 case 'n': c = '\n'; break;                 case 't': c = '\t'; break;             }         }         *target++ = c;     }     *target = '\0'; } 

edit: here's alternative version, using strchr suggested anonymouse. implementation should faster, on long strings relatively few escape characters. posted demonstration of how optimizations can make code more complex , less readable; , consequently less maintainable , more error-prone. detailed discussion, see: http://c2.com/cgi/wiki?optimizelater

void unescape(char *target, const char *source) {     while (*source != '\0')     {         if (*source++ == '\\' && *source != '\0')         {             char c = *source++;             switch (c)             {                 case 'n': c = '\n'; break;                 case 't': c = '\t'; break;             }             *target++ = c;         }         else         {             const char *escape = strchr(source--, '\\');             int numberofchars = escape != null ? escape - source : strlen(source);             strncpy(target, source, numberofchars);             target += numberofchars;             source += numberofchars;         }     }     *target = '\0'; }