So I am just trying to learn C and have decided to program a simple calendar where you can add events etc. It is working almost perfectly however, when it tries to read from the file containing the information, the first line contains some strange characters : �<�}�U1.
Code is as follows:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void createCalendar(char filename[]) {
FILE *cptr;
cptr = fopen(filename, "w");
char dates[177/sizeof(char)] = "";
for(int i = 1; i < 32; i++) {
char strtowrite[7/sizeof(char)] = "";
sprintf(strtowrite, "%d - \n", i);
strcat(dates, strtowrite);
}
fprintf(cptr, "%s", dates);
fclose(cptr);
}
void addToDay(char filename[], int day, char event[]) {
FILE *cptr;
cptr = fopen(filename, "r");
char *line = NULL;
size_t len = 0;
ssize_t read;
char dates[177/sizeof(char) + strlen(event)/sizeof(char)];
int i = 1;
while ((read = getline(&line, &len, cptr)) != -1) {
if (i==day) {
char strtowrite[7/sizeof(char) + strlen(event)/sizeof(char)];
sprintf(strtowrite, "%d - %s\n", i, event);
strcat(dates, strtowrite);
}
else {
strcat(dates, line);
}
i += 1;
}
printf("%s", dates);
fclose(cptr);
cptr = fopen(filename, "w");
fprintf(cptr, "%s", dates);
fclose(cptr);
}
int main() {
createCalendar("january");
addToDay("january", 12, "event");
}
and the first line of output is: í¬_<89>lU1 - (in the file)
Try this
char dates[177/sizeof(char) + strlen(event)/sizeof(char)] = {0};
in your addToDay function when declaring the dates variable. I think that you do not set the memory there, so there might be some junk in that memory location.
Related
I am learning C language. Here is a simple program I did to create 1000 text files.
#include <stdio.h>
#include <string.h>
char * create_filename(char *, char *, int);
int main(void)
{
char prefix_name[50] = "file_no_";
char snum[5];
int no_of_files = 1000;
FILE * fp = NULL;
for (int i = 0; i < no_of_files; i++)
{
fp = fopen( create_filename(prefix_name, snum, i + 1), "w");
fprintf(fp, "This is file no %d", i+1);
fclose(fp);
fp = NULL;
strcpy(prefix_name, "file_no_");
}
return 0;
}
char * create_filename(char * prefix_name, char * snum, int i)
{
sprintf(snum, "%d", i);
strcat(prefix_name, snum);
strcat(prefix_name, ".txt");
return prefix_name;
}
This runs as expected. But I want to know, how can I make this more efficient and as portable as possible. If I want to scale this up to, say 10000 text files, are there other approaches which will be better ?
Thanks
how can I make this more efficient and as portable as possible.
More error checking. Example: a failed fopen() can readily occur.
Realize that a huge amount of time will occur in fopen() and local code likely will have scant time improvements.
Avoid re-writing the prefix.
Use a helper function.
Example:
// Return count of successfully written files.
int create_many_files(const char *prefix, int count, const char *suffix) {
int n;
int len = snprintf(NULL, 0, "%s%n%d%s", prefix, &n, count, suffix);
if (len < 0) {
return 0;
}
// Use len to determine longest name and use a VLA or allocation.
// Consider using a fixed array when len is not too big.
char *filename = malloc((size_t)len + 1u);
if (filename == NULL) {
return 0;
}
strcpy(filename, prefix);
char *offset = filename + n;
for (int i = 0; i < count; i++) {
sprintf(offset, "%d%s", i + 1, suffix);
FILE *fp = fopen(filename, "w");
if (fp == NULL) {
free(filename);
return i;
}
fprintf(fp, "This is file no %d", i + 1);
fclose(fp);
}
free(filename);
return count;
}
Other potential error checks:
prefix == NULL
cout < 0
suffix == NULL
fprintf() < 0
fclose() != 0
I am trying to read the contents of a file and copy those contents into a string which has dynamic memory. However my program keeps allocating only 8 bytes to x. Ultimately I'm trying to create a general function that can read contents from a file and then return the contents as a char. Any help is appreciated.
char* readFile(unsigned long size, char *fileName) {
FILE *file = fopen(fileName, "r");
int c;
if(file != NULL)
{
while(c != EOF){ //calculate size of file
c = fgetc(file); //store character
size++;
}
char *x = (char *)malloc((size) * (sizeof(char))); // Size of x = 8 and I'm not sure why
rewind(file);
printf("\n");
int i = 0;
while(size - 1 > i){ //Reading the files contents to the allocated string
c = fgetc(file); //store character
if(c == EOF){
break;
}
x[i] = c;
i++;
}
fclose(file);
printf("Done Reading");
}
else
{
printf("\nError: Unable to open the file for Reading.\n");
}
rewind(file);
return 0;
}
I get a segmentation fault when I run
char* str = readFile(size, originalFile);
I would use stat to first get the size of your file
stat() retrieves information about the file pointed
to by pathname;
And then I made some tiny modifications to your function to make it work:
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
char* readFile(char *fileName) {
FILE *file;
struct stat st;
if (!(file = fopen(fileName, "r")))
return NULL;
stat(fileName, &st);
unsigned long size = st.st_size;
char *x;
if (!(x = (char *)malloc((size + 1) * (sizeof(char))))) // Size of x = 8 and I'm not sure why
return NULL;
unsigned long i = 0;
while (i < size) //Reading the files contents to the allocated string
x[i++] = getc(file);
x[i] = '\0';
fclose(file);
printf("Done Reading\n");
return x;
}
int main(void) {
char *fileName = "a.txt";
char *res = readFile(fileName);
printf("%s\n", res);
return 0;
}
Don't forget that in C strings are NULL terminated, you need to malloc size+1 to add the final '\0'.
This is (IMHO) an easier way to find the size of the file:
char *readFile(const char *fileName)
{
unsigned long size = 0;
char *x;
FILE *file = fopen(fileName, "r");
int c;
if (file != NULL)
{
fseek(file, 0, SEEK_END); /* SET the position at EOF */
size = ftell(file); /* Record the position at EOF to return size of file */
rewind(file); /* SET position back to Origin */
printf("size detected %ld\n", size); // reads correct size
x = (char *)malloc((size) * (sizeof(char)));
rewind(file);
printf("\n");
int i = 0;
while (size - 1 > i)
{ //Reading the files contents to the allocated string
c = fgetc(file); //store character
if (c == EOF)
{
break;
}
x[i] = c;
i++;
}
fclose(file);
printf("Done Reading\n");
}
else
{
printf("\nError: Unable to open the file for Reading.\n");
return NULL;
}
rewind(file);
return x; // * you need to return x not zero
}
Successfully reads the content of the file:
#include <stdio.h>
#include <stdlib.h>
int main()
{
char *data;
data = readFile("records.txt");
printf("%s\n", data);
return 0;
}
What i need to do, is to take a file of n lines, and for every x lines, create a new file with the lines of the original file. An example would be this:
Original File:
stefano
angela
giuseppe
lucrezia
In this case, if x == 2, 3 file would be created, in order:
First file:
stefano
angela
Second FIle:
giuseppe
lucrezia
Third File:
lorenzo
What i've done so far is this:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define N 10
int getlines(FILE *fp)
{
int c = 0;
int ch;
do{
ch = fgetc(fp);
if(ch == '\n')
{
c++;
}
}while(ch != EOF);
fseek(fp, 0 , SEEK_SET);
return c;
}
int ix = 0;
void Split(FILE *fp, FILE **fpo, int step, int lines, int *mem)
{
FILE **fpo2 = NULL;
char * filename = malloc(sizeof(char)*64);
char * ext = ".txt";
char number[2];
for(int i = ix; i < *mem; i++)
{
itoa(i+1, number,10);
strcpy(filename, "temp");
strcat(filename, number);
strcat(filename, ext);
if(!(fpo[i] = fopen(filename, "w")))
{
fprintf(stderr, "Error in writing\n");
exit(EXIT_FAILURE);
}
}
char ch;
int c = 0;
do{
ch = fgetc(fp);
printf("%c", ch);
if(ch == '\n')
{
c++;
}
if(c >= step)
{
c = 0;
ix++;
if(ix >= *mem && (ix*step) <= lines)
{
*mem = *mem + 1;
fpo2 = realloc(fpo, sizeof(FILE*)*(*mem));
Split(fp, fpo2, step, lines, mem);
}
}
putc(ch, fpo[ix]);
}while(ch != EOF);
}
int main()
{
FILE * fp;
if(!(fp = fopen("file.txt", "r")))
{
fprintf(stderr, "Error in opening file\n");
exit(EXIT_FAILURE);
}
int mem = N;
int lines = getlines(fp);
int step = lines/N;
FILE **fpo = malloc(sizeof(FILE *)*N);
Split(fp, fpo, step, lines, &mem);
exit(EXIT_SUCCESS);
}
I'm stack with segmentation error, i couldn't find the bug doing
gdb myprogram
run
bt
I really appreciate any help.
EDIT:
I've changed some things and now it works, but it creates an additional file that contains strange characters. I need to still adjust some things:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define N 10
int getlines(FILE *fp)
{
int c = 0;
int ch;
do{
ch = fgetc(fp);
if(ch == '\n')
{
c++;
}
}while(ch != EOF);
fseek(fp, 0 , SEEK_SET);
return c;
}
int ix = 0;
void Split(FILE *fp, FILE **fpo, int step, int lines, int *mem)
{
FILE **fpo2 = NULL;
char * ext = ".txt";
for(int i = ix; i < *mem; i++)
{
char * filename = malloc(sizeof(char)*64);
char * number = malloc(sizeof(char)*64);
itoa(i+1, number,10);
strcpy(filename, "temp");
strcat(filename, number);
strcat(filename, ext);
if(!(fpo[i] = fopen(filename, "w")))
{
fprintf(stderr, "Error in writing\n");
exit(EXIT_FAILURE);
}
free(number);
free(filename);
}
char ch;
int c = 0;
do{
ch = fgetc(fp);
printf("%c", ch);
if(ch == '\n')
{
c++;
}
if(c >= step)
{
c = 0;
ix++;
if(ix >= *mem && ((ix-1)*step) <= lines)
{
*mem = *mem + 1;
fpo2 = realloc(fpo, sizeof(FILE*)*(*mem));
Split(fp, fpo2, step, lines, mem);
}
}
putc(ch, fpo[ix]);
}while(ch != EOF);
}
int main()
{
FILE * fp;
if(!(fp = fopen("file.txt", "r")))
{
fprintf(stderr, "Error in opening file\n");
exit(EXIT_FAILURE);
}
int mem = N;
int lines = getlines(fp);
int step = lines/N;
FILE **fpo = malloc(sizeof(FILE *)*N);
Split(fp, fpo, step, lines, &mem);
exit(EXIT_SUCCESS);
}
There are a few problems in your code. But first I think you need to fix the most important thing
int step = lines/N;
Here step is 0 if your input file has less than N lines of text. This is because lines and N both are integer and integer division is rounding down.
I won't fix your code, but I'll help you with it. Some changes I
suggest:
Instead of getlines, use getline(3) from the standard
library.
fseek(fp, 0 , SEEK_SET) is pointless.
In char * filename = malloc(sizeof(char)*64), note that
both arguments to malloc are constant, and the size is arbitrary.
These days, it's safe to allocate filename buffers statically,
either on the stack or with static: char filename[PATH_MAX].
You'll want to use limits.h to get that constant.
Similarly you have no need to dynamically allocate your FILE
pointers.
Instead of
itoa(i+1, number,10);
strcpy(filename, "temp");
strcat(filename, number);
strcat(filename, ext);
use sprintf(filename, "temp%d%s", i+1, ext)
get familiar with err(3) and friends, for your own convenience.
Finally, your recursive Split is -- how shall we say it? -- a nightmare. Your whole program
should be something like:
open input
while getline input
if nlines % N == 0
create output filename with 1 + n/N
open output
write output
nlines++
I want to change my input.txt file to an integer array.
But sadly I keep missing one integer whenever new-line-character is met.
Following is my main()
int main(int args, char* argv[]) {
int *val;
char *STRING = readFile();
val = convert(STRING);
return 0;
}
Following is my file input function
char *readFile() {
int count;
FILE *fp;
fp = fopen("input.txt", "r");
if(fp==NULL) printf("File is NULL!n");
char* STRING;
char oneLine[255];
STRING = (char*)malloc(255);
assert(STRING!=NULL);
while(1){
fgets(oneLine, 255, fp);
count += strlen(oneLine);
STRING = (char*)realloc(STRING, count+1);
strcat(STRING, oneLine);
if(feof(fp)) break;
}
fclose(fp);
return STRING;
}
Following is my integer array function
int *convert(char *STRING){
int *intarr;
intarr = (int*)malloc(sizeof(int)*16);
int a=0;
char *ptr = strtok(STRING, " ");
while (ptr != NULL){
intarr[a] = atoi(ptr);
printf("number = %s\tindex = %d\n", ptr, a);
a++;
ptr = strtok(NULL, " ");
}
return intarr;
}
There are many issues.
This is a corrected version of your program, all comments are mine. Minimal error checking is done for brevity. intarr = malloc(sizeof(int) * 16); will be a problem if there are more than 16 numbers in the file, this should be handled somehow, for example by growing intarr with realloc, similar to what you're doing in readFile.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
char *readFile() {
FILE *fp;
fp = fopen("input.txt", "r");
if (fp == NULL)
{
printf("File is NULL!n");
return NULL; // abort if file could not be opened
}
#define MAXLINELENGTH 255 // define a constant rather than hardcoding "255" at several places
char* STRING;
char oneLine[MAXLINELENGTH];
STRING = malloc(MAXLINELENGTH);
int count = MAXLINELENGTH; // count mus be initialized and better declare it here
assert(STRING != NULL);
STRING[0] = 0; // memory pointed by STRING must be initialized
while (fgets(oneLine, MAXLINELENGTH, fp) != NULL) // correct usage of fgets
{
count += strlen(oneLine);
STRING = realloc(STRING, count + 1);
strcat(STRING, oneLine);
}
fclose(fp);
return STRING;
}
int *convert(char *STRING, int *nbofvalues) { // nbofvalues for returning the number of values
int *intarr;
intarr = malloc(sizeof(int) * 16);
int a = 0;
char *ptr = strtok(STRING, " \n"); // strings may be separated by '\n', or ' '
*nbofvalues = 0;
while (ptr != NULL) {
intarr[a] = atoi(ptr);
printf("number = %s\tindex = %d\n", ptr, a);
a++;
ptr = strtok(NULL, " \n"); // strings are separated by '\n' or ' '
} // read the fgets documentation which
// terminates read strings by \n
*nbofvalues = a; // return number of values
return intarr;
}
int main(int args, char* argv[]) {
int *val;
char *STRING = readFile();
if (STRING == NULL)
{
printf("readFile() problem\n"); // abort if file could not be read
return 1;
}
int nbvalues;
val = convert(STRING, &nbvalues); // nbvalues contains the number of values
// print numbers
for (int i = 0; i < nbvalues; i++)
{
printf("%d: %d\n", i, val[i]);
}
free(val); // free memory
free(STRING); // free memory
return 0;
}
I'm not sure what your requirement is, but this can be simplified a lot because there is no need to read the file into memory and then convert the strings into number. You could convert the numbers on the fly as you read them. And as already mentioned in a comment, calling realloc for each line is inefficient. There is room for more improvements.
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;
}