Making specific word in string uppercase C

Question

Hey all,

I'm trying very hard to figure out a way to parse a string and "highlight" the search term in the result by making it uppercase.

I've tried using strstr and moving a pointer along and "toupper"ing the characters, to no avail.

char * highlight( char *str, char *searchstr ) {

 char *pnt=str;
 int i;

 pnt=strstr(str,searchstr);

 while(pnt){

 printf("ststr retured: %s\n", pnt);

 for(i=0;i<strlen(searchstr);i++) {
  printf("%c",toupper(pnt[i]));
 }
 printf("\n"); 
 pnt=pnt+strlen(searchstr);
 pnt=strstr(pnt,searchstr);

}

 return str;

}

Any advice is greatly appreciated.

Answer 1

You appreciate that the function takes the string as an argument and then returns that same string, while having -not- modified that string? all the function does is print to stdout the capital characters.

At some point, you would need to change the string itself, e.g.;

pnt[i] = toupper( pnt[i] );

Answer 2

Since Schot mentioned every occurrence:

#include <string.h>

char *highlight(char *str, char *searchstr) {

  char *pnt = str;

  while (pnt = strstr(pnt, searchstr)) {
    char *tmp = searchstr;
    while(*(tmp++)) { *pnt = toupper(*pnt); pnt++; }
  }
  return str;

}

int main() {
  char s[] = "hello world follow llollo";
  char search[] = "llo";
  puts(highlight(s, search));
  return 0;
}

output is:

$ ./a.out 
heLLO world foLLOw LLOLLO

Answer 3

Like Blank Xavier said, you probably want to modify the actual string. toupper does not change the value of the character you supply, but returns a new character that is its uppercase version. You have to explicitly assign it back to the original string.

Some additional tips:

• Never do multiple strlen calls on a string that doesn't change, do it once and store the result.
• You can express the promise of not changing searchstr by declaring it as const char *.
• Below is an example with a (in my opinion) easy method of looping through all strstr matches:

#include <string.h>
#include <ctype.h>

char *highlight(char *s, const char *t)
{
    char *p;
    size_t i, len = strlen(t);

    for (p = s; (p = strstr(p, t)); p += len)
        for (i = 0; i < len; i++)
            p[i] = toupper(p[i]);

    return s;
}