Read txt file line by line in C - c

Question

I want to read a txt file, line by line, and each line stores in a different variable:
here is the txt file I want to read
Jenny
Woodbridge Ave
Amber
Exeter street
Michael
Main Street
David
Plainfield ave
and I did like
#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
#include<string.h>
typedef struct info
{
char name[20];
char add[50];
}INFO;
int main(void){
const char *fileName = "test.txt";
FILE *file = fopen(fileName, "r");
INFO* list = (INFO*)malloc(20*sizeof(INFO));
readFromFile(file,list);
fclose(file);
free(list);
return 0;
}
void readFromFile(FILE *file,INFO* list){
int i = 0;
while(!feof(file)){
fscanf(file,"%s %s\n ",(list+i)->name,(list+i)->adds);
i++;
}
}
but I getting
Name: Jenny
Addr: Woodbridge
------------------------------
Name: Ave
Addr: Amber
------------------------------
Name: Exeter
Addr: street
------------------------------
Name: Michael
Addr: Main
------------------------------
Name: Street
Addr: David
------------------------------
Name: Plainfield
Addr: ave
I just edited a little bit
so I need to use fgets to read line by line instead of fscanf() right?

Answer 1

%s specifier reads the input stream until it finds a blank character, in your case as you have 2 words per address, it becomes umbalanced as soon as you try to read it, the second word of the address is read by the next cycle into name, it also has a problem of potencial buffer overflow.
You should use %49[^\n], this specifier reads everything until it finds the newline character, including spaces. The 49 is meant to limit the size of the read line as to avoid the mentioned buffer overflow, in you case you have space for 50 characters, the last character would be for the null terminator.
feof is also not the best way to signal the end of file in this kind of routine, more info in Why is “while ( !feof (file) )” always wrong?.
There are some other issues I address in the comments on the below working sample:
Online demo
int main()
{
//casting malloc may make you program fail, it hides the lack of #include <stdlib.h>
INFO* list = malloc(20 * sizeof *list); //using the the dereferenced variable
//is safer regarding future code refactoring
const char *fileName = "test.txt";
FILE *f = fopen(fileName, "r"); //dont forget to verify the return of fopen
int i = read(f, list);
for (int j = 0; j < i; j++) //test print
{
printf("Name: %s Address: %s\n", list[j].name, list[j].add);
}
}
int read(FILE *file, INFO *list)
{
int i = 0;
//use scanf as stop condition, [] notation is easier to read
//limiting the size in scanf specifiers avoids buffer overflow
while (fscanf(file, "%19s %49[^\n]", list[i].name, list[i].add) == 2)
{
i++;
}
//return i so that you know how many structs were read
return i;
}
Output:
Name: Jenny Address: Woodbridge Ave
Name: Amber Address: Exeter street
Name: Michael Address: Main Street
Name: David Address: Plainfield ave

Answer 2

so I need to use fgets to read line by line instead of fscanf() right?
fscanf(file,"%s %s\n ",.... fails as %s does not read spaces into a string as needed by "Woodbridge Ave" and fails to protect against buffer overrun.
There are many way to solve this task. fgets() is the most clear.
Consider a helper function to read a line and handle fgets() peculiarities of line input. Adjust as needed.
// return 1 on success
// return EOF on end-of-file/input error
// else return 0
int read_line(FILE *file, int sz, char *line) {
if (fgets(line, sz, file) == NULL) {
return EOF; // EOF or rare input error
}
int len = strlen(line);
if (len > 0 && line[len - 1] == '\n') {
line[--len] = '\0'; // lop off potential \n
} else if (len + 1 == sz) { // no \n read, `line` full, so look for rest of input
int ch;
int extra = 0;
while ((ch = fgetc(file)) != '\n' && ch != EOF) {
extra = 1;
}
if (extra) {
return 0; // input too long
}
}
return 1;
}
Now read the file in line pairs into a INFO
int read_INFO(FILE *file, int n, INFO *list) {
int i = 0;
while (i < n
&& read_line(file, sizeof list->name, list[i].name) == 1
&& read_line(file, sizeof list->add, list[i].add) == 1) {
i++;
}
return i;
}
Usage
int n = 20;
INFO *list = malloc(sizeof *list * n);
if (list) {
int number_read = read_INFO(file, n, list);
if (number_read > 0) {
// The happy path
}
}