《C和指针》学习笔记[第9章 字符串、字符和字节]

1.

#define CHAR_SIZE 100
#define NUL '\0'

int main(void){
    char string[CHAR_SIZE];
    fgets(string, sizeof(string)/sizeof(string[0]), stdin);
    
    double string_length;
    int char_num[7] = {0};
    
    string_length = strlen(string);
    
    char *p = string;
    
    while (*p != NUL) {
        if (iscntrl(*p)) {
            char_num[0]++;
        }
        if (isspace(*p)){
            char_num[1]++;
        }
        if (isdigit(*p)){
            char_num[2]++;
        }
        if (islower(*p)){
            char_num[3]++;
        }
        if (isupper(*p)){
            char_num[4]++;
        }
        if (ispunct(*p)){
            char_num[5]++;
        }
        if (!isprint(*p)){
            char_num[6]++;
        }
        p++;
    }
    
    printf("string_length = %.0f\n", string_length);
    printf("cntrl = %d, space = %d, digit = %d, lower = %d, upper = %d, punct = %d no_print = %d\n",
           char_num[0], char_num[1], char_num[2], char_num[3], char_num[4], char_num[5], char_num[6]);
    return EXIT_SUCCESS;
}

2.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <stdarg.h>
#include <ctype.h>
#include "t_c.h"

#define CHAR_SIZE 100
#define NUL '\0'



size_t my_strlen(char *p, int length){
    size_t r_length;
    for (r_length = 0 ; r_length < length; r_length++) {
        if (p[r_length] == NUL) {
            break;
        }
    }
    return r_length;
}


int main(void){
    char string[CHAR_SIZE] = "123456";
    
    printf("%lu\n", my_strlen(string, 10));
    
    return EXIT_SUCCESS;
}

3. 

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <stdarg.h>
#include <ctype.h>
#include "t_c.h"

#define CHAR_SIZE 100
#define NUL '\0'



char *my_strcpy(char *dst, char *src, int lenght){
    char *r_str_point = dst;
    int i;
    for (i = 0; i < lenght; i++) {
        *dst++ = *src++;
        if (*src == NUL) {
            break;
        }
    }
    printf("i = %d, lenght = %d\n", i, lenght);
    if (i == lenght) {
        r_str_point[i] = NUL;
    }
    
    return r_str_point;
    
}

int main(void){
    char string[CHAR_SIZE] = "123456";
    char dst[CHAR_SIZE];
    
    my_strcpy(dst, string, 30);
    printf("%s\n", dst);

    return EXIT_SUCCESS;
}

4.

char *my_strcat(char *dst, char *src, int lenght){
    char *r_str_point = dst;
    
    int i;
    int c_sign = 0;
    for (i = 0; i < lenght; i++) {
        if (*++dst == NUL) {
            c_sign = 1;
        }
        if (c_sign) {
            *dst = *src++;
        }
        if (*src == NUL) {
            break;
        }
    }
    
    if (i == lenght) {
        r_str_point[i] = NUL;
    }
    
    return r_str_point;

}


int main(void){
    char string[CHAR_SIZE] = "123456";
    char dst[CHAR_SIZE] = "abc";
    
    my_strcat(dst, string, 5);
    printf("%s\n", dst);

    return EXIT_SUCCESS;
}

5.