Question

我正在用c编程语言探索系统调用，并尝试复制文件的一些例子。我遇到的问题是，我有一个原始文本文件包含一行“快速棕色狐狸...”要复制，然后结果包含不打算在那里的数据。关于如何解决这个问题我应该知道的任何想法或提示吗？

当我尝试运行代码示例./copy sample.txt new_sample.txt（类似于 cp 命令）时，我在终端上获得此输出：

$./copy sample.txt new_sample.txt
argv[0] = ./copy
argv[1] = sample.txt
argv[2] = new_sample.txt
ERROR: couldn't write whole buffer
Segmentation fault: 11
$

如果终端上有错误，则会创建一个名为new_sample.txt的文件，使用vim编辑器打开它会显示此结果。

快速的棕色狐狸跳过懒狗。 ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^à¯¾dÿ？^ @ ^ @ ^ @ ^ @¾dÿ^^ @ ^ @＆LT;图9b＆gt;有¿¾dÿ^^ @ ^ @Àú½dÿ^^ @ ^ @ ^ _ã¾dÿ^^ @ ^ @@ü½dÿ^^ @ ^ @＆LT;？90＆GT;û½dÿ^？ ^ @ @@ ^ ^û½dÿ？^ @ ^ @ ^ Z ^S¾dÿ^ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @þ^ d ^ A ^ @ ^ @ ^ @ a ^ ^E¾dÿ？^ @ ^ @ ^ @ ^ @ ^ @ ^ @ Y 1？^ @ ^ @ ^G¾dÿ^^ @ ^ @ 0 ^G¾dÿ^^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ C ^ @ ^ @ ^ @pû½dÿ^^ @ ^ @×^Eä|÷并[d？？？？87＆GT; '^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @ ^ @

这是我的示例代码：（filename：copy.c）

#include <sys/stat.h>
#include <fcntl.h>
#include "tlpi_hdr.h" /* contains stdlib, sys/types, stdio.h, unistd, error, string.h */

#ifndef BUF_SIZE /* Allow "cc -D" to override definition */
#define BUF_SIZE 1024
#endif

int main(int argc, char *argv[])
{
    int inputFd;
    int outputFd;
    int openFlags;
    mode_t filePerms;
    ssize_t numRead;
    char buf[BUF_SIZE];

    /* check for the inputs */
    int arg_count=0;
    for (arg_count; arg_count < argc; arg_count++)
        printf("argv[%d] = %s\n", arg_count, argv[arg_count]);

    if (argc != 3 || strcmp(argv[1], "--help") == 0)
        usageErr("%s old-file new-file\n", argv[0]);

    /* open input and outpu files */
    inputFd = open(argv[1], O_RDONLY);
    if (inputFd == -1)
        errExit("opening file %s", argv);

    openFlags = O_CREAT | O_WRONLY | O_TRUNC;
    filePerms = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH; /*rw-rw-rw*/

    outputFd = open(argv[2], openFlags, filePerms);

    if (outputFd == -1)
        errExit("opening file %s", argv[2]);

    /* transfer data until we encounter end of input or an error */

    while ((numRead = read(inputFd, buf, BUF_SIZE)) > 0)
    {
        if (write(outputFd, buf, BUF_SIZE) != numRead)
            fatal("couldn't write whole buffer");
    }

    if (numRead == -1)
        errExit("read");

    if (close(inputFd) == -1)
        errExit("close input");
    if (close(outputFd) == -1)
        errExit("close output");

    exit(EXIT_SUCCESS);
}

Answer 1

您的循环在文件末尾读取太多，因为该文件的长度可能不是BUF_SIZE的倍数。因此，如果文件中有20个字节，则会复制原始的20个字节，加上1004个字节的垃圾（缓冲区中的任何内容）。

执行此操作以将您读取的字节数写入输出：

while ((numRead = read(inputFd, buf, BUF_SIZE)) > 0)
{
    if (write(outputFd, buf, numRead) != numRead)
        fatal("couldn't write whole buffer");
}

使用c语言系统调用复制文件

1 个答案: