fgetc not starting at beginning of file - c [duplicate] - c

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fgetc not starting at beginning of large txt file
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fgetc not starting at beginning of large txt file
I am working in c and fgetc isn't getting chars from the beginning of the file. It seems to be starting somewhere randomly within the file after a \n. The goal of this function is to modify the array productsPrinted. If "More Data Needed" or "Hidden non listed" is encountered, the position in the array, productsPrinted[newLineCount], will be changed to 0. Any help is appreciated.
Update: It works on smaller files, but doesn't start at the beginning of the larger,617kb, file.
function calls up to category:
findNoPics(image, productsPrinted);
findVisible(visible, productsPrinted);
removeCategories(category, productsPrinted);
example input from fgetc():
Category\n
Diagnostic & Testing /Scan Tools\n
Diagnostic & Testing /Scan Tools\n
Hidden non listed\n
Diagnostic & Testing /Scan Tools\n
Diagnostic & Testing /Scan Tools\n
Hand Tools/Open Stock\n
Hand Tools/Sockets and Drive Sets\n
More Data Needed\n
Hand Tools/Open Stock\n
Hand Tools/Open Stock\n
Hand Tools/Open Stock\n
Shop Supplies & Equip/Tool Storage\n
Hidden non listed\n
Shop Supplies & Equip/Heaters\n
Code:
void removeCategories(FILE *category, int *prodPrinted){
char more[17] = { '\0' }, hidden[18] = { '\0' };
int newLineCount = 0, i, ch = 'a', fix = 0;
while ((ch = fgetc(category)) != EOF){ //if fgetc is outside while, it works//
more[15] = hidden[16] = ch;
printf("%c", ch);
/*shift char in each list <- one*/
for (i = 0; i < 17; i++){
if (i < 17){
hidden[i] = hidden[i + 1];
}
if (i < 16){
more[i] = more[i + 1];
}
}
if (strcmp(more, "More Data Needed") == 0 || strcmp(hidden, "Hidden non listed") == 0){
prodPrinted[newLineCount] = 0;
/*printf("%c", more[0]);*/
}
if (ch == '\n'){
newLineCount++;
}
}
}

Answer 1

Let computers do the counting. You have not null terminated your strings properly. The fixed strings (mdn and hdl are initialized but do not have null terminators, so string comparisons using them are undefined.
Given this sample data:
Example 1
More Data Needed
Hidden non listed
Example 2
Keeping lines short.
But as they get longer, the overwrite is worse...or is it?
Hidden More Data Needed in a longer line.
Lines containing "Hidden non listed" are zapped.
Example 3
This version of the program:
#include <stdio.h>
#include <string.h>
static
void removeCategories(FILE *category, int *prodPrinted)
{
char more[17] = { '0' };
char hidden[18] = { '0' };
char mdn[17] = { "More Data Needed" };
char hnl[18] = { "Hidden non listed" };
int newLineCount = 0, i, ch = '\0';
do
{
/*shift char in each list <- one*/
for (i = 0; i < 18; i++)
{
if (i < 17)
hidden[i] = hidden[i + 1];
if (i < 16)
more[i] = more[i + 1];
}
more[15] = hidden[16] = ch = fgetc(category);
if (ch == EOF)
break;
printf("%c", ch); /*testing here, starts rndmly in file*/
//printf("<<%c>> ", ch); /*testing here, starts rndmly in file*/
//printf("more <<%s>> hidden <<%s>>\n", more, hidden);
if (strcmp(more, mdn) == 0 || strcmp(hidden, hnl) == 0)
{
prodPrinted[newLineCount] = 0;
}
if (ch == '\n')
{
newLineCount++;
}
} while (ch != EOF);
}
int main(void)
{
int prod[10];
for (int i = 0; i < 10; i++)
prod[i] = 37;
removeCategories(stdin, prod);
for (int i = 0; i < 10; i++)
printf("%d: %d\n", i, prod[i]);
return 0;
}
produces this output:
Example 1
More Data Needed
Hidden non listed
Example 2
Keeping lines short.
But as they get longer, the overwrite is worse...or is it?
Hidden More Data Needed in a longer line.
Lines containing "Hidden non listed" are zapped.
Example 3
0: 37
1: 0
2: 0
3: 37
4: 37
5: 37
6: 0
7: 0
8: 37
9: 37

Answer 2

You may check which mode you opened the file, and you may have some error-check to make sure you have got the right return value.
Here you can refer to man fopen to get which mode to cause the stream position.
The fopen() function opens the file whose name is the string pointed to
by path and associates a stream with it.
The argument mode points to a string beginning with one of the follow‐
ing sequences (Additional characters may follow these sequences.):
r Open text file for reading. The stream is positioned at the
beginning of the file.
r+ Open for reading and writing. The stream is positioned at the
beginning of the file.
w Truncate file to zero length or create text file for writing.
The stream is positioned at the beginning of the file.
w+ Open for reading and writing. The file is created if it does
not exist, otherwise it is truncated. The stream is positioned
at the beginning of the file.
a Open for appending (writing at end of file). The file is cre‐
ated if it does not exist. The stream is positioned at the end
of the file.
a+ Open for reading and appending (writing at end of file). The
file is created if it does not exist. The initial file position
for reading is at the beginning of the file, but output is
always appended to the end of the file.
And there is another notice, that the file you operated should not more than 2G, or there maybe problem.
And you can use fseek to set the file position indicator.
And you can use debugger to watch these variables to see why there are random value. I think debug is efficient than trace output.

Answer 3

Maybe you can try rewinding the file pointer at the beginning of your function.
rewind(category);
Most likely another function is reading from the same file. If this solves your problem, it would be better to find which other function (or previous call to this function) is reading from the same file and make sure rewinding the pointer won't break something else.
EDIT:
And just to be sure, maybe you could change the double assignment to two different statements. Based on this post, your problem might as well be caused by a compiler optimization of that line. I haven't checked with the standard, but according to best answer the behavior in c and c++ might be undefined, therefore your strange results. Good luck