C语言文件昨日可打开今日找不到原因及字母出现次数统计咨询

Hey there, let's break down your two questions one by one—this stuff happens more often than you might think!

1. Why is the file suddenly not found? #

Even if you didn’t touch your code, there are a handful of common reasons this could happen:

• Changed working directory: When your program runs, it looks for the file in its current working directory. If you ran the code from a different folder today (e.g., your IDE’s run path shifted, or you opened the terminal in a new location), the program can’t locate the file. Try using the full absolute path (like C:\Docs\mytext.txt on Windows or /home/you/mytext.txt on Linux/macOS) instead of just the filename.
• File moved/renamed/deleted: It’s easy to accidentally drag a file to another folder, rename it, or have it cleaned up by a system tool. Double-check the file’s location and exact name to confirm it’s still where you expect.
• Case sensitivity (Linux/macOS): Unix-like systems treat filenames as case-sensitive—MyFile.txt and myfile.txt are two different files. Make sure you’re entering the exact capitalization when prompted.
• Unsafe gets() behavior: The gets() function is risky because it doesn’t handle input limits or trailing spaces well. If you accidentally added a space when typing the filename, gets() would include it, leading the program to look for a file with that extra space. Swap it out for fgets(file_name, sizeof(file_name), stdin) to fix this (we’ll show you how in the code below).

2. How to count occurrences of individual letters? #

To track how many times each letter (a-z) appears, we can use an array to store counts. Here’s a modified version of your code that adds this functionality (plus fixes the gets() issue):

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h> // For tolower() to handle case insensitivity

int main() {
    char ch, file_name[25];
    FILE *fp;
    int letter_counts[26] = {0}; // Initialize all counts to 0

    // Prompt for filename (safer than gets())
    printf("Welche Datei soll aufgerufen werden?\n");
    fgets(file_name, sizeof(file_name), stdin);
    
    // Remove the trailing newline that fgets() adds
    size_t len = 0;
    while (file_name[len] != '\0') {
        if (file_name[len] == '\n') {
            file_name[len] = '\0';
            break;
        }
        len++;
    }

    fp = fopen(file_name, "r"); // Read mode
    if (fp == NULL) {
        perror("Error while opening the file.\n");
        exit(EXIT_FAILURE);
    }

    // Read file content and count letters
    printf("The contents of %s file are:\n", file_name);
    while((ch = fgetc(fp)) != EOF) {
        printf("%c", ch);
        // Convert to lowercase to count uppercase/lowercase as the same
        char lower_ch = tolower(ch);
        // Check if it's a letter a-z
        if (lower_ch >= 'a' && lower_ch <= 'z') {
            letter_counts[lower_ch - 'a']++; // Increment the corresponding count
        }
    }

    // Print the final letter counts
    printf("\n\nLetter occurrence counts:\n");
    for (int i = 0; i < 26; i++) {
        if (letter_counts[i] > 0) {
            printf("%c: %d\n", 'a' + i, letter_counts[i]);
        }
    }

    fclose(fp);
    return 0;
}

Quick breakdown of the changes: #

• letter_counts array: Each index maps to a letter (0 = 'a', 1 = 'b', ..., 25 = 'z') and tracks how many times it appears.
• tolower(): Converts all characters to lowercase so "A" and "a" are counted together (remove this if you want separate counts for uppercase and lowercase).
• fgets() replacement: Fixes the unsafe gets() function and strips the trailing newline that fgets() automatically adds to input.
• Count output: After reading the file, we loop through the array to print only letters that actually appeared.

内容的提问来源于stack exchange，提问作者user12742406