Reading ASCII characters from a file in C

Question

I am printing the first 128 ASCII characters in a file and then trying to read those characters printing their ASCII decimal value.

I tried using fread() and fscanf() functions but both stop after reading first 25 characters.

#include <stdio.h>
int main()
{
    int i;
    char ch;
    FILE *fp;
    fp=fopen("a.txt","w+");
    for(i=0;i<128;i++)
    {
        fprintf(fp,"%c",i);
    }
    fseek(fp,0,SEEK_SET);
    while(fread(&ch, sizeof(char), 1, fp))
        printf("%d\n",ch);
    return 0;
}

I expect the output to be the decimal value of the first 128 ASCII characters but the actual output only have decimal value of first 25 ASCII characters.

Note: ASCII has only 128 characters.

Tom Blodget
– Tom Blodget

2019-02-03 00:06:01 +00:00
Commented Feb 3, 2019 at 0:06 — Tom Blodget
– Tom Blodget, Commented Feb 3, 2019 at 0:06

Weather Vane · Accepted Answer · 2019-02-02 18:03:31Z

3

When you reached 26 the system treated that value as an end-of file marker. All 128 bytes were written but on reading it stopped at value 0x1A (26). This behaviour is for a text file (Windows).

I opened the file in binary mode, and it worked.

fp = fopen("a.txt", "wb+");

If t or b is not given in mode, the default translation mode is defined by the global variable _fmode.

Aside: you should check the return value from fopen. If it is NULL the file could not be opened. You should fclose the file too.

answered Feb 2, 2019 at 18:03

Weather Vane

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2 Comments

EsmaeelE Over a year ago

Why the system treated 26 as an end-of file marker?

Weather Vane Over a year ago

@EsmaeelE it is also the value of the Crtl-Z key press, used to indicate EOF from the keyboard (Windows). That value is by definition, in the same way that 13 or Ctrl-M is carriage return.

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