how do I read non .txt file in c programming?

Question

I want to read a c file from another c program. and print it line by line. But I got some problem. here is my code, the file to be read and the output i'm getting in terminal.

my Code

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{
    char sourcefilename[100];
    char targetfilename[100];
    int counter = 0;
    int lower_limit = 10;
    char *line = NULL;
    char *temp = NULL;
    int is_multilinecomment = 0;

    FILE *source = fopen("hello.c", "r");
    FILE *target = fopen("newcode.c", "w");

    char ch = fgetc(source);
    while (ch != EOF)
    {
        // printf("%c", ch);
        if (ch == '\n')
        {
            counter = 0;
            printf("%s\n", line);
            free(line);
            line = NULL;
        }
        else
        {
            temp = (char *)realloc(line, counter * sizeof(char));
            if (!temp)
            {
                free(line);
                line = NULL;
            }
            line = temp;
            line[counter] = ch;
            counter++;
            // printf("%s", line);
        }
        // printf("helo");
        ch = fgetc(source);
    }
    return 0;
}

hello.c

I'm trying to read this file

#include <stdio.h>
#include <string.h>
// this is a single line comment
int main()
{
    char var[500];
    printf("Enter a name of a variable : ");
    scanf("%s", var);

    if (!((var[0] >= 'a' && var[0] <= 'z') || (var[0] >= 'A' && var[0] <= 'Z') || var[0] == '_'))
    {
        printf("%s is not valid variable.\n", var);
        return 0;
    }
    // this is another single line comment
    for (int i = 1; i < strlen(var); i++)
    {
        if (!((var[i] >= 'a' && var[i] <= 'z') || (var[i] >= 'A' && var[i] <= 'Z') || var[i] == '_' || (var[i] >= '0' && var[i] <= '9')))
        {

            printf("%s is not valid variable.\n", var);
            return 0;
        }
    }
    /*
    this is a multi line
    comment */

    printf("%s is valid variable.\n", var);

    return 0;
}

output i'm getting

#include <stdio.h>\Progr�
#include <string.h>
// this is a single line comment`�
int main()�
{�
    char var[500];e line/
    printf("Enter a name of a variable : ");{~
    scanf("%s", var);ame/
    if (!((var[0] >= 'a' && var[0] <= 'z') || (var[0] >= 'A' && var[0] <= 'Z') || var[0] == '_'))�
    {
        printf("%s is not valid variable.\n", var);
        return 0;s is nok�_z~
    }
    // this is another single line comment
    for (int i = 1; i < strlen(var); i++)
    {
        if (!((var[i] >= 'a' && var[i] <= 'z') || (var[i] >= 'A' && var[i] <= 'Z') || var[i] == '_' || (var[i] >= '0' && var[i] <= '9')))
 _�

you can notice here i'm getting some unwanted characters at the end of each line. and also last part of the hello.c is ignored.

please help !!!

Your title is misleading. C files are the same as .txt files. The file extension does not tell anything. — Gerhardh, Feb 25 '22 at 14:25
`int fgetc(FILE *stream);` catch return value in an integer; coz often EOF is not an 8-bit character. — जलजनक, Feb 25 '22 at 14:27
You might take a look at [Why is “while ( !feof (file) )” always wrong?](https://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong) — Gerhardh, Feb 25 '22 at 14:27
`(var[0] >= 'a' && var[0] <= 'z')`? Use [`islower()`](https://port70.net/~nsz/c/c11/n1570.html#7.4.1.7) instead. And `isupper()` for upper-case checks. — Andrew Henle, Feb 25 '22 at 14:44

Gerhardh · Accepted Answer · 2022-02-25T14:47:15.747

You have multiple issues in your code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{
    char sourcefilename[100];
    char targetfilename[100];
    int counter = 0;
    int lower_limit = 10;
    char *line = NULL;
    char *temp = NULL;
    int is_multilinecomment = 0;

    FILE *source = fopen("hello.c", "r");
    FILE *target = fopen("newcode.c", "w");

    char ch = fgetc(source);

Function fgetc returns an int. This is required to detect EOF. Do not use char.

    while (ch != EOF)

See Why is “while ( !feof (file) )” always wrong? for details

    {
        // printf("%c", ch);
        if (ch == '\n')
        {
            counter = 0;
            printf("%s\n", line);

If you hit an empty line, you do not have any memory allocated for line and it contains NULL, causing undefined behaviour.

In any case you do not have a terminating 0 byte in your line buffer. This means it is not a valid string and passing that character array to printf again causes undefined behaviour.

            free(line);
            line = NULL;
        }
        else
        {
            temp = (char *)realloc(line, counter * sizeof(char));

You start with counter=0 for each line. You allocate 0 bytes for first character. Instead of allocating memory for your string + 1 byte for terminating \0 byte, you allocate 2 bytes less.

            if (!temp)
            {
                free(line);
                line = NULL;
            }
            line = temp;
            line[counter] = ch;

If condition (!temp) was true above, you still assign temp to line and dereference it, causing undefined behaviour.

            counter++;
            // printf("%s", line);
        }
        // printf("helo");
        ch = fgetc(source);
    }
    return 0;
}

Some more issues, not related with weird characters:

You do not write your output to target file.
You do not close your files.
A proper signature for main should be int main (void). Empty parameter list in function definition should not be used nowadays.
Most of your variables in main are unused.
Not all included headers are actually required.

how do I read non .txt file in c programming?

my Code

hello.c

output i'm getting

1 Answers1