my task is to write a struct which reads data from file and realloc more memory if needed.
So Far I have done this:
The Struct:
typedef struct myprog
{
int id;
char name[100];
int price;
}myprog;
Read Function:
myprog* readFromFile(FILE* fP, char fileName[], myprog* reg, int* size)
{
fP = fopen(fileName, "r"); //Open Input File as read
if (fP == NULL) //If File is not found, do nothing
{
printf("File does not exist.");
}
else //Else read file line by line
{
printf("\nReading from File");
int x = 0;
char line[100];
char* split;
char* args[4];
while (fgets(line, 100, fP)) //Read the first line
{
if (x == MAX) //If Max Size is reached, increase it twice
{
int new_size = MAX * 2;
reg = (struct vara*)realloc(reg, new_size * sizeof(struct vara)); //Even if i comment these lines the code works :O
}
split = strtok(line, " "); //Split the line on space delimiter i.e {"1", "apple", "10"}
args[0] = split;
int i = 1;
while (split != NULL)
{
split = strtok(NULL, " ");
args[i] = split;
i++;
}
if (i != 3) //Checking if the args size is three
{
//Copy from args to struct
reg[x].id = atoi(args[0]); //Copy Number
strcpy(reg[x].name, args[1]); //Copy Name
reg[x].price = atoi(args[2]); //Copy Balance
x++;
}
}
(*size) = x;
printf("\nReading Completed!");
fclose(fP);
}
return reg;
}
Main Function:
void main()
{
char fileName[100];
FILE* fP = NULL;
printf("Enter file Name : ");
scanf("%s", fileName);
myprog* reg = malloc(MAX * sizeof * reg); //#define MAX 1
int size = 0;
reg = readFromFile(fP, fileName, reg, &size);
//Some Code below
}
The Problem I am facing:
When I run the code with MAX defined with 1, it reads any number of products from file without any memory leak errors. It even works without the realloc, can you please help me identify my mistake?
The data in input file is like this:
1 prod_a 15
2 prod_b 20
I have the following .csv file containing information about the song, artist, release year (if specified) and number of listens:
Look What The Cat Dragged In,Poison,,Look What The Cat Dragged In by Poison,1,0,1,0
Nothin' But A Good Time,Poison,1988,Nothin' But A Good Time by Poison,1,1,21,21
Something To Believe In,Poison,1990,Something To Believe In by Poison,1,1,1,1
Talk Dirty To Me,Poison,1978,Talk Dirty To Me by Poison,1,1,1,1
A Salty Dog,Procol Harum,1969,A Salty Dog by Procol Harum,1,1,1,1
A Whiter Shade of Pale,Procol Harum,1967,A Whiter Shade of Pale by Procol Harum,1,1,3,3
Blurry,Puddle of Mudd,2001,Blurry by Puddle of Mudd,1,1,1,1
Amie,Pure Prairie League,,Amie by Pure Prairie League,1,0,4,0
Another One Bites the Dust,Queen,1980,Another One Bites the Dust by Queen,1,1,102,102
Bicycle Race,Queen,1978,Bicycle Race by Queen,1,1,3,3
Kiss You All Over,Kiss,1978,Kiss You All Over by Kiss,1,1,5,5
The name of the file and the desired year should be given as command line arguments, and the program should print all songs from that specific year.
e.g.: ./a.out music.csv 1978
Output:
Talk dirty to me
Bicycle Race
Kiss You All Over
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#define MAX 300
typedef struct {
char song[101], *artist, *line;
long int year;
} music;
int checkYear(char *word)
{
for (int i = 0; i < strlen(word); i++) {
if (!isdigit(word[i]))
return 0;
}
return 1;
}
int main(int argc, char **argv)
{
FILE *fin = fopen(argv[1], "r");
if (!fin)
{
printf("Error opening the file.\n");
return 1;
}
char buf[MAX];
//int nLines = 0; //count the number of lines
//music *array = NULL;
while( fgets(buf, MAX, fin))
{
buf[strcspn(buf, "\n")] = '\0'; // strip the trailing newline
char *word = strtok(buf, ",");
while (word)
{
//printf("Word is : %s\n", word);
if (checkYear(word))
{
//printf("Year : %s\n", word);
music *array = (music *)malloc(sizeof(music));
char *p;
array->year = strtol(word, &p, 10);
if (array->year == atoi(argv[2]))
{
//printf("Year : %ld\t%d\n", array->year, atoi(argv[2]));
if (scanf("%100[^,]", array->song) == 1)
{
printf("Song : %s\n", array->song);
}
}
}
word = strtok(NULL, ",");
}
}
//printf("I've read %d lines\n", nLines);
fclose(fin);
return 0;
}
So far, it's going decent, I can extract the specified year from each line, but now I just need to print the name of the song from those lines (the first token on the line). I thought about using scanf("%[^,]") to read and print everything up until the first comma but it's just stuck in an endless loop. Could you give me an idea? Thanks in advance!
There are multiple problems in the code:
you do not check that enough arguments were passed on the command line, potentially invoking undefined behavior if not.
you do not need to allocate a music structure: you can just parse the first 3 fields, check the year and output the name of the song directly.
strtok() is inappropriate to split fields from a csv file because it treats a sequence of separators as a single separator, which is incorrect and causes invalid parsing if some fields are empty.
sscanf("%[^,]", ...) will fail to convert an empty field.
To split the fields from the csv line, I recommend you use a utility function that behaves like strtok_r() but tailored for csv lines. A simplistic version will stop on , and \n and replace these with a null byte, returning the initial pointer and updating the pointer for the next field. A more advanced version would also handle quotes.
Here is a modified version:
#include <stdio.h>
#include <string.h>
#define MAX 300
char *get_field(char **pp) {
char *p, *start;
for (p = start = *pp; *p; p++) {
if (*p == ',' || *p == '\n') {
*p++ = '\0';
break;
}
}
*pp = p;
return start;
}
int main(int argc, char *argv[]) {
char buf[MAX];
FILE *fin;
char *filename;
char *select_year;
if (argc < 3) {
printf("Missing arguments\n");
return 1;
}
filename = argv[1];
select_year = argv[2];
fin = fopen(filename, "r");
if (!fin) {
printf("Error opening the file %s.\n", filename);
return 1;
}
while (fgets(buf, sizeof buf, fin)) {
char *p = buf;
char *song = get_field(&p);
char *artist = get_field(&p);
char *year = get_field(&p);
if (!strcmp(year, target_year)) {
printf("%s\n", song);
}
}
fclose(fin);
return 0;
}
regarding: scanf("%[^,]") this consumes (upto but not including) the comma.
So the next instruction needs to be something like getchar() to consume the comma. Otherwise, on the next loop nothing will be read because the first character in stdin is that same comma.
I was just creating simple implementation where I read input.txt file which has one line of code containing two numbers separated by space (e.g. 4 4).
I was trying to separate them by delimiting with space first.
And I was trying to use the first value as a size of char array.
However it keeps causing segmentation fault but I have no idea.
int main(int argc, char **argv){
int number;
int i = 0;
char *token;
char buf[100];
int tempNum[2];
// Open file
FILE * fPointer;
fPointer = fopen("input.txt", "r");
// Read first line
fgets(buf, 1024, fPointer);
token = strtok(buf, " ");
number = atoi(token);
char charArray[number];
while(token != NULL){
tempNum[i] = atoi(token);
token = strtok(NULL, "\n");
printf("%d\n", tempNum[i]);
i++;
}
If I comment out "char charArray[number]" it does not cause segmentation fault. If I comment out only the while loop, it does not cause segmentation fault. But I cannot figure out why it is causing the segmentation in the first place. Please help.
Thank you in advance.
Something like this?
#include <stdlib.h>
#include <stdio.h>
#include <stdio.h>
#include <string.h>
#define BUF_SIZE 1024
#define MAX_INPUT 2
int main(int argc, char **argv) {
char *token = NULL;
char *next_token = NULL;
char buf[BUF_SIZE];
long tempNum[MAX_INPUT] = { 0 };
const char *delim = " ";
char * end = NULL;
// Init vars
memset(buf, 0, BUF_SIZE);
// Open file
FILE * fPointer = fopen("input.txt", "r");
if (fPointer == NULL) {
return 1;
}
// Read first line
if (fgets(buf, BUF_SIZE, fPointer) == NULL) {
fclose(fPointer);
return 2;
}
// Parse line
token = strtok_s(buf, delim, &next_token);
for (int i = 0;((i < MAX_INPUT) && (token != NULL)); i++){
tempNum[i] = strtol(token, &end, 10);
if (*end != NULL){
printf("error in %s\n", token);
} else {
printf("%d\n", tempNum[i]);
}
token = strtok_s(NULL, delim, &next_token);
}
fclose(fPointer);
return 0;
}
Im new to c and am trying to understand pointers.
here I am opening a file and reading the lines given. Im trying to append these lines into an array and return it from the function. I dont seem to be appending or accessing the array correctly. output[count] = status; gives an error with mismatched char and char *.
Im essentially trying to get an array with a list of words given by a file where each element in the array is a word.
char *fileRead(char *command, char output[255]) {
int count = 0;
char input[255];
char *status;
FILE *file = fopen(command, "r");
if (file == NULL) {
printf("Cannot open file\n");
} else {
do {
status = fgets(input, sizeof(input), file);
if (status != NULL) {
printf("%s", status);
strtok(status, "\n");
// add values into output array
output[count] = status;
++count;
}
} while (status);
}
fclose(file);
return output;
}
I access fileRead via:
...
char commandArray[255];
char output[255];
int y = 0;
char *filename = "scriptin.txt";
strcpy(commandArray, fileRead(filename, output));
// read from array and pass into flag function
while (commandArray[y] != NULL) {
n = flagsfunction(flags, commandArray[y], sizeof(buf), flags.position, &desc, &parentrd, right, left, lconn);
y++;
...
Example of Read from file Line by line then storing nonblank lines into an array (array of pointer to char (as char*))
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
//for it does not exist because strdup is not a standard function.
char *strdup(const char *str){
char *ret = malloc(strlen(str)+1);
if(ret)
strcpy(ret, str);
return ret;
}
//Read rows up to 255 rows
int fileRead(const char *filename, char *output[255]) {
FILE *file = fopen(filename, "r");
if (file == NULL) {
perror("Cannot open file:");
return 0;
}
int count = 0;
char input[255];
while(count < 255 && fgets(input, sizeof(input), file)) {
char *line = strtok(input, "\n");
if(line)//When it is not a blank line
output[count++] = strdup(line);//Store replica
}
fclose(file);
return count;
}
int main(void){
char *output[255];//(`char *` x 255)
int number_of_read_line = fileRead("data.txt", output);
for(int i = 0; i < number_of_read_line; ++i){
printf("%s\n", output[i]);
free(output[i]);//Discard after being used
}
return 0;
}
I'm trying to read in a file with a couple hundred integers, some positive, some negative and store them in an array. They have to be read in as a string using strtok, though. I keep getting a segmentation fault and I'm not sure why. The count is to figure out how many total integers are in the file.
/*Input file looks like this:
718321747 -1828022042
-1665405912 -175307986
-53757018 -1551069786 525902369
-1945908378 853648883
*/
int main(int argc, char* argv[])
{
char buffer[50];
char* token;
int count = 0;
int num = 0;
int arr[MAX_SIZE];
if (argc != 2)
{
printf("Invalid number of arguments\n");
return 0;
}
FILE* fptr = fopen(argv[1], "r");
//open file
if (fptr == NULL)
{
printf("Unable to open file\n");
return 0;
}
while(fgets(buffer, 50, fptr))
//to get the file line by line
{
token = strtok(buffer, "\n\t ");
//find first token
num = atoi(token);
//convert it to an int
arr[count] = num;
//store in array
count++;
while(token != NULL)
//get rest of tokens and convert to int
{
token = strtok(buffer, "\n\t ");
num = atoi(token);
arr[count] = num;
count++;
}
}
return 0;
}
You never check if the token was found in the string, you must check that strtok() didn't return NULL before trying to call atoi().
Then you keep scanning the same string with strtok() passing the string in each iteration, that's also wrong, you should pass NULL after the first time.
I would also recommend to use strtol() instead of atoi() to check if the conversion was successful.
Check this code, i fixed it
#include <stdio.h>
#include <stdlib.h>
#define MAX_SIZE 1000 /* ? whatever value you think is good. */
int main(int argc, char* argv[])
{
char buffer[50];
int count = 0;
int arr[MAX_SIZE];
if (argc != 2)
{
printf("Invalid number of arguments\n");
return 0;
}
FILE* fptr = fopen(argv[1], "r");
//open file
if (fptr == NULL)
{
printf("Unable to open file\n");
return 0;
}
//to get the file line by line
while ((fgets(buffer, 50, fptr) != NULL) && (count < MAX_SIZE))
{
char *pointer;
char *token;
pointer = buffer;
while (((token = strtok(pointer, "\n\t ")) != NULL) && (count < MAX_SIZE))
{
char *endptr;
arr[count] = strtol(token, &endptr, 10);
printf("%d\n", arr[count]);
if (*endptr != '\0')
printf("error: could not convert %s to integer\n", token);
else
count++;
pointer = NULL;
}
}
return 0;
}
I am not sure it will work for you because I haven't seen the structure of your input data, but I am sure it will not cause a segmentation fault.