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feofThis article will introduce several ways to use functions in C language .

Use feofthe function to check the end-of-file indicator on a file stream in C language

feofThe function is part of the C standard input/output library and is defined in <stdio.h>the header file. feofThe function checks the end-of-file indicator on the given file stream and EOFreturns a non-zero integer if it is set. It takes FILEa pointer as its only argument.

In the following example, we demonstrate that when getlinereading a file line by line using the read_line function, the function is called until feofread_line returns zero, meaning that the file stream has not yet been reached EOF. Note that we verify the return value of the read_line function in the conditional statement and only call read_line() getlineif it succeeds .printf

#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>

const char* filename = "input.txt";

int main(void) {

    FILE* in_file = fopen(filename, "r");
    if (!in_file) {
        perror("fopen");
        exit(EXIT_FAILURE);
    }

    struct stat sb;
    if (stat(filename, &sb) == -1) {
        perror("stat");
        exit(EXIT_FAILURE);
    }

    char *contents = NULL;
    size_t len = 0;

    while (!feof(in_file)) {
        if (getline(&contents, &len, in_file) != -1) {
            printf("%s", contents);
        }
    }

    fclose(in_file);
    exit(EXIT_SUCCESS);
}

feofUse the and functions in C ferrorto test the valid position of a file stream

Additionally, before we read the contents of a file, we can use feofto test the position of the file stream. In this case, we freadread the file using a call to read the file, which statretrieves the size of the file using the function call. Note that the buffer that stores the read bytes is mallocallocated on the heap using the function. Additionally, we include the function in a conditional statement ferror, EOFalong with the indicator to test the state of the file stream error.

#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>

const char* filename = "input.txt";

int main(void) {

    FILE* in_file = fopen(filename, "r");
    if (!in_file) {
        perror("fopen");
        exit(EXIT_FAILURE);
    }

    struct stat sb;
    if (stat(filename, &sb) == -1) {
        perror("stat");
        exit(EXIT_FAILURE);
    }

    char* file_contents = malloc(sb.st_size);
    if (!feof(in_file) && !ferror(in_file))
        fread(file_contents, 1, sb.st_size, in_file);
    printf("read data: %s\n", file_contents);

    free(file_contents);

    fclose(in_file);
    exit(EXIT_SUCCESS);
}

ferroris also part of the I/O library and can be FILEcalled on a pointer object. It returns a non-zero indicator if the error bit is set on the file stream. Note that all three examples print filenamethe contents of the file specified by the variable. In the previous sample code, we used printfthe function to output the stored contents, but a more error-prone method is fwriteto call , which can print a given number of bytes to FILEthe stream specified by the fourth parameter.

#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>

const char* filename = "input.txt";

int main(void) {

    FILE* in_file = fopen(filename, "r");
    if (!in_file) {
        perror("fopen");
        exit(EXIT_FAILURE);
    }

    struct stat sb;
    if (stat(filename, &sb) == -1) {
        perror("stat");
        exit(EXIT_FAILURE);
    }

    char* file_contents = malloc(sb.st_size);
    if (!feof(in_file) && !ferror(in_file))
        fread(file_contents, 1, sb.st_size, in_file);
    fwrite(file_contents, 1, sb.st_size, stdout);

    free(file_contents);

    fclose(in_file);
    exit(EXIT_SUCCESS);
}