c - 在 C 中解析命令行参数

Question

我正在尝试编写一个程序，可以在 C 中逐行、逐字或逐字符地比较两个文件。它必须能够读取命令行选项 -l、-w、-i 或 --...

• 如果选项是-l，它逐行比较文件。
• 如果选项是-w，它逐字比较文件。
• 如果选项是--，它会自动假定下一个参数是第一个文件名。
• 如果选项是-i，它会以不区分大小写的方式比较它们。
• 默认逐个字符比较文件。

只要 -w 和 -l 不同时输入并且没有更多选项，输入多少次并不重要或少于两个文件。

我什至不知道从哪里开始解析命令行参数。

这就是我为所有内容想出的代码。我还没有完全检查错误，但我是否以过于复杂的方式编写了东西？

/*
 * Functions to compare files.
 */
int compare_line();
int compare_word();
int compare_char();
int case_insens();

/*
 * Program to compare the information in two files and print message saying
 * whether or not this was successful.
 */
int main(int argc, char* argv[])
{
    /* Loop counter */
    size_t i = 0;

    /* Variables for functions */
    int caseIns = 0;
    int line = 0;
    int word = 0;

    /* File pointers */
    FILE *fp1, *fp2;

    /*
     * Read through command-line arguments for options.
     */
    for (i = 1; i < argc; i++)
    {
        printf("argv[%u] = %s\n", i, argv[i]);
        if (argv[i][0] == '-')
        {
             if (argv[i][1] == 'i')
             {
                 caseIns = 1;
             }
             if (argv[i][1] == 'l')
             {
                 line = 1;
             }
             if (argv[i][1] == 'w')
             {
                 word = 1;
             }
             if (argv[i][1] == '-')
             {
                 fp1 = argv[i][2];
                 fp2 = argv[i][3];
             }
             else
             {
                 printf("Invalid option.");
                 return 2;
             }
        }
        else
        {
           fp1(argv[i]);
           fp2(argv[i][1]);
        }
    }

    /*
     * Check that files can be opened.
     */
    if(((fp1 = fopen(fp1, "rb")) ==  NULL) || ((fp2 = fopen(fp2, "rb")) == NULL))
    {
        perror("fopen()");
        return 3;
    }
    else
    {
        if (caseIns == 1)
        {
            if(line == 1 && word == 1)
            {
                printf("That is invalid.");
                return 2;
            }
            if(line == 1 && word == 0)
            {
                if(compare_line(case_insens(fp1, fp2)) == 0)
                        return 0;
            }
            if(line == 0 && word == 1)
            {
                if(compare_word(case_insens(fp1, fp2)) == 0)
                    return 0;
            }
            else
            {
                if(compare_char(case_insens(fp1,fp2)) == 0)
                    return 0;
            }
        }
        else
        {
            if(line == 1 && word == 1)
            {
                printf("That is invalid.");
                return 2;
            }
            if(line == 1 && word == 0)
            {
                if(compare_line(fp1, fp2) == 0)
                    return 0;
            }
            if(line == 0 && word == 1)
            {
                if(compare_word(fp1, fp2) == 0)
                    return 0;
            }
            else
            {
                if(compare_char(fp1, fp2) == 0)
                    return 0;
            }
        }
    }
    return 1;

    if(((fp1 = fclose(fp1)) == NULL) || (((fp2 = fclose(fp2)) == NULL)))
    {
        perror("fclose()");
        return 3;
    }
    else
    {
        fp1 = fclose(fp1);
        fp2 = fclose(fp2);
    }
}

/*
 * Function to compare two files line-by-line.
 */
int compare_line(FILE *fp1, FILE *fp2)
{
    /* Buffer variables to store the lines in the file */
    char buff1 [LINESIZE];
    char buff2 [LINESIZE];

    /* Check that neither is the end of file */
    while((!feof(fp1)) && (!feof(fp2)))
    {
        /* Go through files line by line */
        fgets(buff1, LINESIZE, fp1);
        fgets(buff2, LINESIZE, fp2);
    }

    /* Compare files line by line */
    if(strcmp(buff1, buff2) == 0)
    {
        printf("Files are equal.\n");
        return 0;
    }
    printf("Files are not equal.\n");
    return 1;
}

/*
 * Function to compare two files word-by-word.
 */
int compare_word(FILE *fp1, FILE *fp2)
{
    /* File pointers */
    FILE *fp1, *fp2;

    /* Arrays to store words */
    char fp1words[LINESIZE];
    char fp2words[LINESIZE];

    if(strtok(fp1, " ") == NULL || strtok(fp2, " ") == NULL)
    {
        printf("File is empty. Cannot compare.\n");
        return 0;
    }
    else
    {
        fp1words = strtok(fp1, " ");
        fp2words = strtok(fp2, " ");

        if(fp1words == fp2words)
        {
            fputs(fp1words);
            fputs(fp2words);
            printf("Files are equal.\n");
            return 0;
        }
    }
    return 1;
}

/*
 * Function to compare two files character by character.
 */
int compare_char(FILE *fp1,FILE *fp2)
{
    /* Variables to store the characters from both files */
    int c;
    int d;

    /* Buffer variables to store chars */
    char buff1 [LINESIZE];
    char buff2 [LINESIZE];

    while(((c = fgetc(fp1))!= EOF) && (((d = fgetc(fp2))!=EOF)))
    {
        if(c == d)
        {
            if((fscanf(fp1, "%c", buff1)) == (fscanf(fp2, "%c", buff2)))
            {
                printf("Files have equivalent characters.\n");
                return 1;
                break;
            }
        }

    }
    return 0;
}

/*
 * Function to compare two files in a case-insensitive manner.
 */
int case_insens(FILE *fp1, FILE *fp2, size_t n)
{
    /* Pointers for files. */
    FILE *fp1, *fp2;

    /* Variable to go through files. */
    size_t i = 0;

    /* Arrays to store file information. */
    char fp1store[LINESIZE];
    char fp2store[LINESIZE];

    while(!feof(fp1) && !feof(fp2))
    {
        for(i = 0; i < n; i++)
        {
            fscanf(fp1, "%s", fp1store);
            fscanf(fp2, "%s", fp2store);

            fp1store = tolower(fp1store);
            fp2store = tolower(fp2store);

            return 1;
        }
    }
    return 0;
}

Answer 1

据我所知，在 C 中解析命令行参数的三种最流行的方法是:

• Getopt(#include <unistd.h> 来自 POSIX C 库)，它可以解决简单的参数解析任务。如果您对 bash 有点熟悉，bash 的内置 getopt 基于 GNU libc 中的 Getopt。
• Argp(来自 GNU C 库的 #include <argp.h>)，它可以解决更多复杂的任务并处理诸如以下的事情:
  • -? , --help 帮助消息，包括电子邮件地址
  • -V , --version 版本信息
  • --usage 使用信息
• 自己做，我不推荐给别人的程序，因为太多可能出错或质量下降。忘记“--”以停止选项解析的常见错误只是一个例子。

GNU C 库文档有一些很好的 Getopt 和 Argp 示例。

• http://www.gnu.org/software/libc/manual/html_node/Getopt.html
• http://www.gnu.org/software/libc/manual/html_node/Argp.html

使用 Getopt 的示例

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
    bool isCaseInsensitive = false;
    int opt;
    enum { CHARACTER_MODE, WORD_MODE, LINE_MODE } mode = CHARACTER_MODE;

    while ((opt = getopt(argc, argv, "ilw")) != -1) {
        switch (opt) {
        case 'i': isCaseInsensitive = true; break;
        case 'l': mode = LINE_MODE; break;
        case 'w': mode = WORD_MODE; break;
        default:
            fprintf(stderr, "Usage: %s [-ilw] [file...]\n", argv[0]);
            exit(EXIT_FAILURE);
        }
    }

    // Now optind (declared extern int by <unistd.h>) is the index of the first non-option argument.
    // If it is >= argc, there were no non-option arguments.

    // ...
}

使用Argp的例子

#include <argp.h>
#include <stdbool.h>

const char *argp_program_version = "programname programversion";
const char *argp_program_bug_address = "<your@email.address>";
static char doc[] = "Your program description.";
static char args_doc[] = "[FILENAME]...";
static struct argp_option options[] = { 
    { "line", 'l', 0, 0, "Compare lines instead of characters."},
    { "word", 'w', 0, 0, "Compare words instead of characters."},
    { "nocase", 'i', 0, 0, "Compare case insensitive instead of case sensitive."},
    { 0 } 
};

struct arguments {
    enum { CHARACTER_MODE, WORD_MODE, LINE_MODE } mode;
    bool isCaseInsensitive;
};

static error_t parse_opt(int key, char *arg, struct argp_state *state) {
    struct arguments *arguments = state->input;
    switch (key) {
    case 'l': arguments->mode = LINE_MODE; break;
    case 'w': arguments->mode = WORD_MODE; break;
    case 'i': arguments->isCaseInsensitive = true; break;
    case ARGP_KEY_ARG: return 0;
    default: return ARGP_ERR_UNKNOWN;
    }   
    return 0;
}

static struct argp argp = { options, parse_opt, args_doc, doc, 0, 0, 0 };

int main(int argc, char *argv[])
{
    struct arguments arguments;

    arguments.mode = CHARACTER_MODE;
    arguments.isCaseInsensitive = false;

    argp_parse(&argp, argc, argv, 0, 0, &arguments);

    // ...
}

自己动手的示例

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{   
    bool isCaseInsensitive = false;
    enum { CHARACTER_MODE, WORD_MODE, LINE_MODE } mode = CHARACTER_MODE;
    size_t optind;
    for (optind = 1; optind < argc && argv[optind][0] == '-'; optind++) {
        switch (argv[optind][1]) {
        case 'i': isCaseInsensitive = true; break;
        case 'l': mode = LINE_MODE; break;
        case 'w': mode = WORD_MODE; break;
        default:
            fprintf(stderr, "Usage: %s [-ilw] [file...]\n", argv[0]);
            exit(EXIT_FAILURE);
        }   
    }
    argv += optind;

    // *argv points to the remaining non-option arguments.
    // If *argv is NULL, there were no non-option arguments.

    // ...
}   

免责声明:我是 Argp 的新手，该示例可能包含错误。