Languages such as Python have the replace(s, old, new [,maxreplace])
method which not only replaces a substring but also allows one to limit the number of replacements made. How can I implement this in C without use of Regex
? It is preferred that the cstring is not modified and can be of any length including 0. This was what I tried. I would like this function to have a parameter max_replacements
such that if and only if it equates to 0, all occurrences are replaced.
char *strnrep(char *haystack, char needle, char replacement, int max_replacements) {
char buf[strlen(haystack) 1];
int count = 0;
strcpy(buf, haystack);
for (unsigned j = 0; j < strlen(buf); j) {
if (buf[j] == needle) count ;
}
int j = 0;
if (max_replacements == 0) {
max_replacements = count;
}
while (j < max_replacements) {
for (int i = 0; buf[i] != '\0'; i ) {
if (buf[i] == needle) {
buf[i] = replacement;
break;
}
}
j ;
}
return strdup(buf);
}
But only works for char
rather than char*
or char[]
...
NOTE This question is NOT duplicate to what one of the commenters is suggesting. I am asking for a specified number of occurrences rather than all.
CodePudding user response:
Updating previous replace solution
Don't look for all occurence, stop if you reach the limit with something like:
if (count >= max)
break;
// You must free the result if result is non-NULL.
char *str_replace(const char *orig, char *rep, char *with, int max) {
char *result; // the return string
const char *ins; // the next insert point
char *tmp; // varies
int len_rep; // length of rep (the string to remove)
int len_with; // length of with (the string to replace rep with)
int len_front; // distance between rep and end of last rep
int count; // number of replacements
// sanity checks and initialization
if (!orig || !rep)
return NULL;
len_rep = strlen(rep);
if (len_rep == 0)
return NULL; // empty rep causes infinite loop during count
if (!with)
with = "";
len_with = strlen(with);
// count the number of replacements needed
ins = orig;
for (count = 0; tmp = strstr(ins, rep); count) {
ins = tmp len_rep;
if (count >= max)
break;
}
tmp = result = malloc(strlen(orig) (len_with - len_rep) * count 1);
if (!result)
return NULL;
// first time through the loop, all the variable are set correctly
// from here on,
// tmp points to the end of the result string
// ins points to the next occurrence of rep in orig
// orig points to the remainder of orig after "end of rep"
while (count--) {
ins = strstr(orig, rep);
len_front = ins - orig;
tmp = strncpy(tmp, orig, len_front) len_front;
tmp = strcpy(tmp, with) len_with;
orig = len_front len_rep; // move to next "end of rep"
}
strcpy(tmp, orig);
return result;
}
int main(void)
{
const char* input = "foo bar one bar two bar three bar";
char *replace = str_replace(input, "bar", "john", 2);
printf("before: %s\nafter: %s\n", input, replace);
free(replace);
return 0;
}
will output
before: foo bar one bar two bar three bar
after: foo john one john two bar three bar