How To Read Integers From A File Line By Line In C?

If you want to read integers from a file line by line in c, it’s pretty simple. You loop through each line of text in the file and read each character individually.

You can either use POSIX’s getline function or do it manually by buffering chunks of the line and reading them from there. Just remember to free the line buffer when you’re done.

Fgetc()

fgetc() is a C function that reads an integer from a file line by line. This function is slow and should not be used on large files. It also should not be called on a file with many lines of data because it will take too long to process the line.

Unlike text files, which are logically a sequence of lines separated by newlines, binary files are a stream of bytes. The I/O subsystem handles these streams of bytes very differently.

Several file-handling functions can be used in the C programming language to read and process a file. These functions include fgets(), fgetc(), and fprintf().

The fgetc() function reads the next character from an input stream and returns it as an unsigned char cast to an int or EOF at the end of the file or error, as appropriate. It then increments the associated file pointer (if defined), pointing to the next character.

Another file-handling function is fgets() which reads a string or a line from an input stream and stores it in a well-defined string variable. The function terminates its reading session when it encounters a newline character.

A gets () function requires three parameters, among which str points to the character that will be read from a given stream; num is the maximum number of characters to be read from a stream, and the stream is a pointer to the FILE type specifying the input stream. On success, the str parameter sets str to point to the character that will be read from the stream, and on failure, it sets str to NULL.

The fgetc function is similar to the get macro, except it may be implemented as a subroutine rather than a macro. It may be necessary to use a subroutine because the macro does not evaluate the stream more than once.

Fgets()

Fgets is a file-handling function in C that reads data line by line from a given file. The function stores data in the char str variable until either (n-1) characters have been read, a newline character has been read, or the end of the file is reached.

Gets returns a pointer to the string read from the file and then appends the terminating null character at the end of the string. It also stops reading once the newline character is detected.

The fgets() function can be used to read an integer from a stream of characters, and it is designed to ensure that no truncation errors occur during the reading process. It also limits the size of the string to n bytes.

It is important to note that a null pointer is returned when no characters are being read or when an error occurs. The stream parameter can be replaced by stdin when reading from standard input.

Another difference between fgets and gets is that fgets accepts a FILE object for the stream from which it is reading instead of just a stdin argument. This can be useful when reading many characters from the same stream.

fgets also allows you to specify the maximum size of the string it should read using an argument called n. This can be a helpful way to ensure that the stream is not too long for you to handle.

In addition to the n argument, fgets also allows you to specify that the last (ending) newline character should be included in the string it is copied to. This can be handy if you have data that must not end on a newline character but do not want to lose any other characters.

Finally, fgets also stops reading when n-1 characters have been read, a newline has been read, or the end of the file has been reached. If this happens, it will return a pointer to s.

fgets is similar to scan, except that it allows you to set the maximum length of str. This can be a helpful way to avoid the possibility of a buffer overflow that could cause an error during the reading process.

Feof()

If you want to read integers from a file line by line in c, you must use the function of. It is defined in the cstdio> header and tests whether or not the end of a stream has been reached. It returns a nonzero value if the end of the stream has been reached and zero if the end of the stream has not been reached.

Streams are special objects in the studio library that can be used for input and output operations. Each stream is associated with a file in the host environment that is open for reading or writing, depending on whether the stream is opened in read or write mode. In either case, the file will be closed when it is no longer used.

The studio library provides several functions to indicate the end of a stream. These include food, clearer, rewind, and seek. Each function sets the end-of-file indicator associated with the stream pointed to by the stream pointer, which can be cleared using the rewind, seek, or clearer functions.

These functions also test if the end-of-file indicator is set on the stream before performing any other operation. Again, this is a very important step in the stream’s lifecycle.

This is because the stream’s internal position indicator will point to the end-of-file for a subsequent operation, even if the operation does not reach that point. This indicates that the previous operation did not attempt to read past the end of the stream but was just following a position-pointer error.

In addition, several standard I/O routines will return a value when they try to read a block of data from a file, which is another way of indicating that the end of a file has been reached. For example, the function scanf will return a value that reflects how many values were assigned to variables before the file’s end-of-file was reached or when a format string mismatch occurred between the variable’s argument and its next value.

Moreover, both scanf and fscanf will return a value if the end of a file has been reached or if there is a type mismatch between the next value and the variable’s next argument. The fscanf function is particularly useful in testing the validity of format strings.

Fprintf

The C standard I/O library provides several convenient routines for reading and writing data one character at a time. These functions include print and scarf.

The print function converts and formats its arguments under the control of a format string writes them to a file descriptor, and then returns the count of characters written. The function also returns an errmsg if it writes an error message.

fprintf takes as its first argument a file descriptor, a pointer to a storage location for a formatted output stream, and as its second and subsequent arguments an implementation-defined character sequence defining a pointer. This sequence is then replaced by the values of the formatted arguments as specified in the format string.

Each format string contains C language conversion specifications, including notation, alignment, significant digits, and field width. The format string may contain escape characters to represent non-printing characters, such as newlines and tabs.

For decimal conversions (%i, %d, %u, %f, %g, or %G), precision specifies the minimum number of digits to be printed. If this number cannot specify the value length to be printed, the result is padded with blank spaces and trailing zeros. The radix character appears only if the value has been converted to a radix that supports it.

fprintf also supports nonstandard subtype specifiers for the conversion characters %o, %u, %x, and %X. These can be used to format a double as a decimal number, an infinity value, or a NaN value.

Another important characteristic of the format string is its minimum field width. For numeric conversions a, A, e, E, f, and g, this is the minimum number of digits to be written after the decimal point; for other conversions, it is the maximum number of significant digits. The resulting value is not truncated if it is longer than the maximum number of digits, even when the precision is 0.

The fprintf family also supports nonstandard characters to represent the results of a fractional conversion. These include the f, e, and E style of converting a double in the style f or e.

If you want to read integers from a file line by line in C.

You Can Use The Following Steps:

• Open the file using fopen(). This function takes two parameters: the file’s name and the mode you want to open it (e.g., “r” for reading). It returns a FILE pointer.

FILE *fp;

fp = open(“filename.txt”, “r”);

• Check if the file was opened successfully. If fopen() returns NULL, it means an error opened the file.

if (fp == NULL) {

    printf(“Error opening file\n”);

    exit(1); }

• Use fgets() to read a line from the file. This function takes three parameters: a buffer to store the line, the maximum number of characters to read, and the FILE pointer.

char buffer[100];

fgets(buffer, 100, fp);

• Use sscanf() to extract the integers from the line. This function takes two parameters: the string to parse and a format string specifying the data types to extract. In this case, you can use %d to extract integers.

int num1, num2;

sscanf(buffer, “%d %d”, &num1, &num 2);

• Repeat steps 3-4 for each line in the file. You can use a loop to read the file until the end.

while (fgets(buffer, 100, fp) != NULL) {

    int num1, num2;

    sscanf(buffer, “%d %d”, &num1, &num 2);

    // do something with the integers. }

• Close the file using close () when you’re done reading it.
• close(fp);

Here’s The Complete Code:

#include <stdio.h>

#include <stdlib.h>

int main() {

    FILE *fp;

    fp = fopen(“filename.txt”, “r”);

    if (fp == NULL) {

        printf(“Error opening file\n”);

        exit(1); }

    char buffer[100];

    while (fgets(buffer, 100, fp) != NULL) {

        int num1, num2;

        sscanf(buffer, “%d %d”, &num1, &num 2);

        // do something with the integers }

    close(fp);

    return 0; }

Note that this code assumes that each line in the file contains two integers separated by a space. If the file contains a different format, you must adjust the sscanf() format string accordingly. Also, ensure that the buffer size is large enough to hold the longest line in the file.

FAQ’s

How to read an entire line in C?

The fgets function is typically used to read a line of text in C, which is OK if you know in advance how lengthy a line of text might be. At the GitHub repository for this post, you can access all the code samples and the input file.

How to read file from second line in C?

until the character n is encountered, read each character till the second line is reached. The first line must be read and ignored in order to read from the second, then the second and successive lines must be read and processed as necessary. Think about utilising fgets ()

How do I read nth line of a file in C using file handling?

Hence, by invoking “fgets,” you may read each line. While you keep track of the number of lines, throw away any that are fewer than n. Stop reading when you get to the nth line and then send the line’s content back.

How to get a line from a file in C?

The fopen() method must be used to open a file stream in order to read from a text file in C. Once a file stream has been opened, you may use the fgets() function to read the file line by line.

What does read () do in C?

A file’s previously written data is read using the read() function. read() will return bytes with a value of 0 if any part of a normal file that comes before the end of the file has not been written.