c - I am getting "pointer being freed was not allocated" -

i reading stdin. since not know length of read, have use malloc.

i getting pointer being freed not allocated

sometimes, happens before free(final), before free(tmp).

i check both pointers correctly non null after creating them , before making free. can pin point doing wrong ?

total_size = 0; final = (char *)malloc(sizeof(char) * 1); if (!final) {     printf("error allocating memory final\n");     return (null); } while ((ret = read(0, buf, buf_size)) > 0) {     tmp = (char *)malloc(sizeof(char) * ft_strlen(final));     if (!tmp)     {         printf("error allocating memory tmp\n");         return (null);     }     strcpy(tmp, final);     if (final)         free(final);     buf[ret] = '\0';     total_size = total_size + ret;     final = (char *)malloc(sizeof(char) * total_size);     if (!final)     {         printf("error allocating memory final\n");         return (null);     }     final = strcat(tmp, buf);     if (tmp)         free(tmp); } return (final); 

this problem you:

final = (char *)malloc(sizeof(char) * total_size); 

[...]

final = strcat(tmp, buf); 

you leaking allocated memory , aliasing *final , *tmp. can thereafter free one of them, must not afterward free other without first reassigning point valid dynamically-allocated block.

overall, looks going lot of unnecessary trouble tmp. far can tell, you're trying increase size of block final points, , that's realloc() for:

size_t desired_size = total_size + ret + 1;  // need space terminator char *tmp = realloc(final, desired_size); if (!tmp) {     perror("error allocating more memory final");     // realloc() not free pointer on failure; @ least glibc's doesn't     free(final);     return (null); } final = tmp;  buf[ret] = '\0';  // strcat wasteful if know destination string's length strcpy(final + total_size, buf); total_size += ret; 

the reallocated block may or may not start in same place original, realloc() takes care of copying data if necessary.