C++命令行文件复制程序：新文件创建后无法写入及多文件异常

Let's walk through the issues in your code one by one and get things working correctly:

Key Problems Identified #

1. Main Function Parameter Mix-Up #

You swapped the names of main's parameters! The first parameter is argc (count of command-line arguments), and the second is argv (array of argument strings). Your code uses int argv, const char* argc[], which breaks the loop that processes target files. Plus, you hardcoded i < 10 instead of using argc to iterate over all provided target files—this is why you couldn't process multiple missing files.

2. Broken Exit Logic in WriteFile #

The second while loop in WriteFile has a fatal logical error:

while (input.at(0) != 'Y' || input.at(0) != 'y' || input.at(0) != '1') {
    exit(0);
}

This condition is always true—no character can be equal to Y, y, and 1 at the same time. So even if the user chooses to create the file, this loop runs and exits the program immediately, skipping the content write step.

Additionally, you used a while loop for the user input check when a single if is sufficient (the user only needs to answer once).

3. Unchecked File Pointer After Creation #

If file creation fails, fptr remains nullptr, but the code still tries to write to it, which will cause a crash.

Fixed Code #

Here's the corrected version with all issues addressed:

#include <iostream>
#include <cstdio>
#include <string>
#include <cstdlib>

char* ReadFile(const char* filename) {
    // Assume this function works correctly as stated
    static char buffer[1024]; // Example placeholder, adjust size as needed
    FILE* f = fopen(filename, "r");
    if (f) {
        fread(buffer, 1, sizeof(buffer)-1, f);
        buffer[sizeof(buffer)-1] = '\0';
        fclose(f);
    }
    return buffer;
}

void WriteFile(const char* filename, const char* data) {
    if (!data) {
        std::cout << "Error: No data to write to " << filename << std::endl;
        return;
    }

    FILE* fptr = fopen(filename, "r+");
    if (fptr) {
        std::cout << filename << " opened successfully.\n";
    } else {
        std::cout << "\nFile " << filename << " not found! Do you want to create one?\n";
        std::cout << "Type Y, y or 1 to create, any other key to exit\n";
        std::string input;
        std::cin >> input;

        // Exit if user doesn't want to create the file
        if (input.at(0) != 'Y' && input.at(0) != 'y' && input.at(0) != '1') {
            std::cout << "Exiting without creating " << filename << std::endl;
            exit(0);
        }

        // Attempt to create the file
        fptr = fopen(filename, "w");
        if (!fptr) {
            std::cout << "Error creating " << filename << std::endl;
            return;
        }
        std::cout << filename << " created successfully\n";
    }

    // Write data only if file pointer is valid
    if (fptr) {
        while (*data) {
            fputc(*data, fptr);
            ++data;
        }

        if (fclose(fptr) == 0) {
            std::cout << filename << " closed successfully\n";
        } else {
            std::cout << "Error closing " << filename << std::endl;
        }
    }
}

int main(int argc, char* argv[]) {
    // Validate input arguments
    if (argc < 3) {
        std::cout << "Usage: " << argv[0] << " <source-file> <target-file1> [target-file2] ...\n";
        return 1;
    }

    const char* fileBuffer = ReadFile(argv[1]);
    if (!fileBuffer) {
        std::cout << "Error reading source file " << argv[1] << std::endl;
        return 1;
    }

    // Process all target files sequentially
    for (int i = 2; i < argc; ++i) {
        WriteFile(argv[i], fileBuffer);
    }

    return 0;
}

What Changed? #

1. Fixed Main Parameters: Corrected argc and argv names, and now loop over all target files using i < argc instead of a hardcoded limit. Added a usage prompt if the user runs the program with too few arguments.
2. Rewrote User Input Logic: Replaced the broken while exit check with a single if statement using && instead of ||, so the program only exits if the user doesn't want to create the file.
3. Added Safety Checks: Added checks for data being null and fptr being valid before writing, preventing crashes from invalid pointers.
4. Cleaned Up Flow: Simplified the file creation logic to avoid unnecessary loops, making the code easier to follow.

Now when you run main.exe file.txt todo.txt app.txt foo.txt:

• Existing target files will have their contents overwritten with the source file data.
• Missing target files will prompt the user to create them, and if confirmed, the source data will be written to the new file.
• All target files (existing or new) will be processed in sequence.

内容的提问来源于stack exchange，提问作者Juned Khan