Using strdup into malloc reserved space

Question

I've never used malloc to store more than values but I have to use strdup to order the lines of an input file and I dont get a way to make it work.

I though using strdup() to get a pointer to each line and later, put each one into a space according to the number of lines reserved with malloc().

I dont know if I have to do it like reserved memory was an array to pointers, I mean using char** and later put each pointer to each strdup into reserved space.

I though something like this:

char **buffer;
char *pointertostring;
char *line; // line got using fgets

*buffer = (char*)malloc(sizeof(char*));
pointertostring = strdup(line);

I don't know what to do after that, I don't even know if this is correct, in that case, what should I do to store the pointer to the string in a position of buffer?

Regards

Answer 1

If I understand your requirement correctly. You'll have to do something like:

char **buffer; 
char line[MAX_LINE_LEN]; // line got using fgets
int count; // to keep track of line number.    

// allocate one char pointer for each line in the file.
buffer = (char**)malloc(sizeof(char*) * MAX_LINES); 

count = 0; // initilize count.

// iterate till there are lines in the file...read the line using fgets.
while(fgets(line,MAX_LINE_LEN,stdin)) {
    // copy the line using strdup and make the buffer pointer number 'count' 
    // point to it
    buffer[count++] = strdup(line);
}
....
....
// once done using the memory you need to free it.
for(count=0;count<MAX_LINES;count++) {
     free(buffer[count]);
}
....
....