Question

I’m trying to write a function that shifts all the elements in an array of strings up by one.

void shift_frags(char **frags, int frag_len, int cur) {     int i;     for(i = cur; i < frag_len-1; i++)     {         if(strlen(frags[i+1]) > strlen(frags[i]))             frags[i] = realloc(frags[i], strlen(frags[i+1])*sizeof(char));         strcpy(frags[i], frags[i+1]);     }      free(frags[frag_len-1]); } 

This is giving me the error: ‘realloc(): invalid next size: …’ Each array is dynamically allocated to be the size of a string read from a file. Shouldn’t I be able to dynamically allocate new array sizes since my frags parameter is an array of pointers?

Thanks

Answer 1

Since as you say the array is just an array of pointers, you do not need to perform any reallocations. You just need to copy the pointers themselves. A simple call to memmove or something similar in the portion of the array is all that is required.

Something approximating this.

void shift_frags(char **frags, int frag_len, int cur) {   free(frags[frag_len]);   memmove(frags+cur+1, frags+cur, (frag_len-cur) * sizeof(char*)); }