How do I scan text into a string within a function? - c

Question

So I have to scan text from a file into an array, but I am only allowed to use scanf() to achieve this. In the file, there are 22 lines and the longest line is 455 characters long. When I compile, I get various warnings. I have been trying to find a solution but nothings seems to help my list of warnings and errors.
#include <stdio.h>
#include <stdlib.h>
#define NUM_ROWS 22
#define LENGTH_OF_LONGEST_LINE 455
void textInit(char array[]);
int main(void) {
char patty [NUM_ROWS][LENGTH_OF_LONGEST_LINE];
textInit(patty[NUM_ROWS][LENGTH_OF_LONGEST_LINE]);
return 0;
}
void textInit(char array[]) {
int x = 0;
for (x = 0; x < 22; ++x) {
scanf("%455s", array[x]);
}
return;
}
The errors I recieve are:
StPat.c: In function âmainâ:
StPat.c:14:4: warning: passing argument 1 of âtextInitâ makes pointer from
integer without a cast [enabled by default]
textInit(patty[NUM_ROWS][LENGTH_OF_LONGEST_LINE]);
^
StPat.c:9:6: note: expected âchar *â but argument is of type âcharâ
void textInit(char array[]);
^
StPat.c: In function âtextInitâ:
StPat.c:26:7: warning: format â%sâ expects argument of type âchar *â, but
argument 2 has type âintâ [-Wformat=]
scanf("%455s", array[x]);

Answer 1

LENGTH_OF_LONGEST_LINE should be 456 to allow space for the \0 terminator.
The body of the function textInit() expects a 2d array, but the function signature only indicates an array of chars. You should also pass the dimensions of the array to the function, rather than rely on global constants.
When you call the textInit() function, you are attempting to pass a char instead of a 2d array (really, a 2d array name in a function call decays to a pointer to an array). The attempted access is out of bounds.
Finally, in the textInit() function, avoid using magic numbers, as you have in the loop in this function. And you should use size_t for array indices, as it is an unsigned integer type guaranteed to hold any array index.
Here is a modified version of your code:
#include <stdio.h>
#include <stdlib.h>
#define NUM_ROWS 22
#define LENGTH_OF_LONGEST_LINE 456
void textInit(char array[][LENGTH_OF_LONGEST_LINE], size_t rows, size_t cols);
int main(void)
{
char patty [NUM_ROWS][LENGTH_OF_LONGEST_LINE];
textInit(patty, NUM_ROWS, LENGTH_OF_LONGEST_LINE);
return 0;
}
void textInit(char array[][LENGTH_OF_LONGEST_LINE], size_t rows, size_t cols)
{
size_t x = 0;
for (x = 0; x < rows; ++x) {
scanf("%455s", array[x]);
}
return;
}

Answer 2

In addition to the nul-byte catch by Mr. Bowling, you can also make use of fgets to take the input. If you would like to init the entire array, you can pass an array of pointers to type char LENGTH_OF_LONGEST_LINE and initialize the entire array at once. For example:
#include <stdio.h>
#include <string.h>
enum { MAXROWS = 22, MAXLINE = 456 };
size_t textinit (char (*a)[MAXLINE], size_t rows, size_t cols);
int main(void) {
size_t i, n;
char patty [MAXROWS][MAXLINE] = {""};
n = textinit (patty, MAXROWS, MAXLINE);
for (i = 0; i < n; i++)
printf (" string[%2zu] : %s\n", i, patty[i]);
return 0;
}
size_t textinit (char (*a)[MAXLINE], size_t rows, size_t cols)
{
size_t n = 0;
while (n < rows && fgets (a[n], cols, stdin))
{
size_t len = strlen (a[n]); /* get lenght */
if (a[n][len - 1] == '\n') /* check for '\n' */
a[n][--len] = 0; /* overwrite with nul-byte */
n++;
}
return n; /* return number of strings read */
}
Note, that fgets reads up to and including the '\n', so you remove the newline by getting the length of each string read, then testing for, and overwriting the '\n' with a nul-terminating character 0 (or the equivalent '\0').
Also note, if you are on windows, replace size_t with unsigned and %2zu in the printf with simply %2u.