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I use getline function to read a line from STDIN . The prototype of getline is: ssize_t getline(char **lineptr, size_t *n, FILE *stream); I use this as a test program which get from http://www.crasseux.com/books/ctutorial/getline.html#getline #include <stdio.h> #include <stdlib.h> #include <string.h> int main(int atgc, char *argv[]) { int bytes_read = 1; int nbytes = 10; char *my_string; my_string = (char *)malloc(nbytes+1); puts("Please enter a line of text"); bytes_read = getline(&my_string, &nbytes, stdin); if (bytes_read == -1) { puts ("ERROR!"); } else { puts ("You typed:"); puts (my_string); } return 0; } This works fine. My doubts are? Why use char **lineptr instead char *lineptr as a parameter of function getline ? Why it is wrong when I use the following code: char **my_string; bytes_read = getline(my_string, &nbytes, stdin); I am confused with * and & . Here is part of warnings: testGetline.c: In function ‘main’: testGetline.c:34: warning: pointer targets in passing argument 2 of ‘getline’ differ in signedness /usr/include/stdio.h:671: note: expected ‘size_t * __restrict__’ but argument is of type ‘int *’ testGetline.c:40: warning: passing argument 1 of ‘putchar’ makes integer from pointer without a cast /usr/include/stdio.h:582: note: expected ‘int’ but argument is of type ‘char *’ I use GCC version 4.4.5 (Ubuntu/Linaro 4.4.4-14ubuntu5).

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