如何使用POSIX函数从C语言的文件中计算多个字符？

Question

我正在尝试使用标准的POSIX函数编写一个包含文件和字符串的程序，该程序会计算该字符串包含的文件中的所有字符。

例如，如果用户写：

count.exe x.txt abcd

程序将计算每个字符的数量：文件x.txt中的a，b，c，d

示例消息：

Number of 'a' characters in 'x.txt' file is: 4
Number of 'b' characters in 'x.txt' file is: 9
Number of 'c' characters in 'x.txt' file is: 7
Number of 'd' characters in 'x.txt' file is: 0

到目前为止，我得到的代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>

#define BUFSIZE     1024


void exit_sys(const char* msg)
{
    perror(msg);
    exit(EXIT_FAILURE);
}

void exit_fail(const char* msg)
{
    fprintf(stderr, "%s\n", msg);
    exit(EXIT_FAILURE);
}

int get_count(char* p, size_t size, char c)
{
    int count = 0;
    size_t i;

    for (i = 0; i < size; ++i)
        if (p[i] == c)
            ++count;

    return count;
}


void run_count_characters_application(int argc, char** argv)
{
    int fd;
    char c;
    char buf[BUFSIZE];
    int n;
    int count;

    if (argc != 3)
        exit_fail("usage: ./mycounter file character");

    if (strlen(argv[2]) < 0)
        exit_fail("You have to give at least one character");

    c = argv[2][0];

    if ((fd = open(argv[1], O_RDONLY)) < 0)
        exit_sys("open");

    count = 0;


    while ((n = read(fd, buf, BUFSIZE)) > 0)
        count += get_count(buf, n, c);

    if (n < 0)
        exit_sys("read");


    printf("Count:%d\n", count);

    close(fd);
}

int main(int argc, char** argv)
{
    run_count_characters_application(argc, argv);

    return 0;
}

到目前为止，我在这段代码中遇到的问题是它仅计数一个字符（仅第一个字符），我想知道如何使其读取并计算在命令中写入的其他字符，谢谢提前:)

Answer 1

[您只计算一个字符argv [2] [0]，即argv [2]是“ abcd”，那么您只在数“ a”。

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

struct char_count {
    char c;
    int count;
};

static char read_char(FILE *file)
{
    char c = 0;

    fscanf(file, "%c", &c);
    return c;
}

static void print_count(struct char_count *cc, int len)
{
    int i;

    for (i = 0; i < len; i ++) {
        printf("%c-%d ", cc[i].c, cc[i].count);
    }
    printf("\n");
}

int main(int argc, char **argv)
{
    FILE *file;
    char c = 0;
    struct char_count *cc;
    int len = 0;
    int i;

    if (argc != 3)
        return printf("Invalid arguments !\n");
    file = fopen(argv[1], "r");
    if (!file)
        return printf("Could not open file !\n");
    len = strlen(argv[2]);
    if (len < 1)
        return printf("At least one char required !\n");
    cc = calloc(len, sizeof(struct char_count));
    if (!cc) {
        printf("Error allocation memory !\n");
        return 1;
    }
    for (i = 0; i < len; i++) {
        cc[i].c = argv[2][len - (i + 1)];
    }
    while(!feof(file)) {
        c = read_char(file);
        for (i = 0; i < len; i++) {
            if (c == cc[i].c)
                cc[i].count++;
        }
    }
    printf("\n");
    print_count(cc, len);
    return 0;
}