字符函数和字符串函数(上)-C语言详解

CSDN的各位友友们你们好,今天千泽为大家带来的是C语言中字符函数和字符串函数的详解,掌握了这些内容能够让我们更加灵活的运用字符串,
接下来让我们一起走进今天的内容吧!
写这篇文章需要在 cplusplus.com 上大量截图,十分不易!
如果对您有帮助的话希望能够得到您的支持和帮助,我会持续更新的!

0.前言

C语言中对字符和字符串的处理很是频繁，但是C语言本身是没有字符串类型的，字符串通常放在

常量字符串中或者字符数组中。

字符串常量适用于那些对它不做修改的字符串函数.

首先,我们将本次要介绍的函数分一下类

长度不受限制的字符串函数

strcpy

strcat

strcmp

长度受限制的字符串函数介绍

strncpy

strncat

strncmp

1.函数介绍

strcpy

例子

/* strcpy example */
#include 
#include 

int main ()
{
  char str1[]="Sample string";
  char str2[40];
  char str3[40];
  strcpy (str2,str1);
  strcpy (str3,"copy successful");
  printf ("str1: %s\nstr2: %s\nstr3: %s\n",str1,str2,str3);
  return 0;
}

输出：

str1: Sample string
str2: Sample string
str3: copy successful

模拟实现strcpy

#include
#include
//1.参数顺序
//2.函数的功能，停止条件
//3.assert
//4.const修饰指针
//5.函数返回值
//6.题目出自《高质量C/C++编程》书籍最后的试题部分
//返回的是目标空间的起始地址
#include
char * my_strcpy(char * dest, const char* src)
{
    char * ret = dest;
    assert(dest!=NULL);
    assert(src != NULL);
    while ((*dest++ = *src++))
    {
        ;
    }
    return ret;
}
int main()
{
    char arr1[] = "hehe";
    char arr2[20] = { 0 };
    my_strcpy(arr2, arr1);
    printf("%s\n", arr2);
    return 0;
}

友友们记得动手实践!!!

strcat

官方例子

/* strcat example */
#include 
#include 

int main ()
{
  char str[80];
  strcpy (str,"these ");
  strcat (str,"strings ");
  strcat (str,"are ");
  strcat (str,"concatenated.");
  puts (str);
  return 0;
}

输出

these strings are concatenated.

模拟实现strcat

#include
#include
char* my_strcat(char* dest, const char* src)
{
    char* ret = dest;
    assert(dest != NULL);
    assert(src != NULL);
    //找目标空间的\0
    while (*dest!='\0')
    {
        dest++;
    }
    //拷贝
    while ((*dest++ = *src++))
    {
        ;
    }
    return ret;
}
int main()
{
    char arr1[20] = "hello ";
    char arr2[] = "world";
    //追加
    my_strcat(arr1, arr2);
    printf("%s\n", arr1);
    return 0;
}

strcmp

官方例子

#include 
#include 

int main ()
{
  char key[] = "apple";
  char buffer[80];
  do {
     printf ("Guess my favorite fruit? ");
     fflush (stdout);
     scanf ("%79s",buffer);
  } while (strcmp (key,buffer) != 0);
  puts ("Correct answer!");
  return 0;
}

输出

Guess my favourite fruit? orange
Guess my favourite fruit? apple
Correct answer!

模拟实现strcmp

#include
#include
#include
int my_strcmp(const char* str1, const char* str2)
{
    assert(str1 != NULL);
    assert(str2 != NULL);
    while (*str1 == *str2)
    {
        if (*str1 == '\0')
        {
            return 0;
        }
        str1++;
        str2++;
    }
    if (*str1 > *str2)
    {
        return 1;
    }
    else
    {
        return -1;
    }
}
 
int main()
{
    char arr1[] = "abcdef";
    char arr2[] = "bbcdef";
    int ret = my_strcmp(arr1, arr2);
    printf("%d\n", ret);
    return 0;
}

strncpy

官方例子

/* strncpy example */
#include 
#include 

int main ()
{
  char str1[]= "To be or not to be";
  char str2[40];
  char str3[40];

  /* copy to sized buffer (overflow safe): */
  strncpy ( str2, str1, sizeof(str2) );

  /* partial copy (only 5 chars): */
  strncpy ( str3, str2, 5 );
  str3[5] = '\0';   /* null character manually added */

  puts (str1);
  puts (str2);
  puts (str3);

  return 0;
}

输出

To be or not to be To be or not to be To be

模拟实现strncpy

#include
#include
#include
int main()
{
    char arr1[] = "abcdef";
    char arr2[5] = { 0 };
    strncpy(arr2, arr1, 3);
    printf("%s\n", arr2);
    return 0;
}

strncat

官方例子

/* strncat example */
#include 
#include 

int main ()
{
  char str1[20];
  char str2[20];
  strcpy (str1,"To be ");
  strcpy (str2,"or not to be");
  strncat (str1, str2, 6);
  puts (str1);
  return 0;
}

输出

To be or not

模拟实现strncat

#include
#include
#include
int main()
{
    char arr1[20] = "hello \0xxxxxxxx";
    char arr2[] = "world";
    strncat(arr1, arr2, 3);
    printf("%s\n", arr1);
    return 0;
}

strncmp

官方例子

/* strncmp example */
#include 
#include 

int main ()
{
  char str[][5] = { "R2D2" , "C3PO" , "R2A6" };
  int n;
  puts ("Looking for R2 astromech droids...");
  for (n=0 ; n<3 ; n++)
    if (strncmp (str[n],"R2xx",2) == 0)
    {
      printf ("found %s\n",str[n]);
    }
  return 0;
}

输出

Looking for R2 astromech droids... found R2D2 found R2A6

模拟实现strncmp

#include
#include
#include
int main()
{
    char arr1[] = "abcdef";
    char arr2[] = "abcq";
    int ret = strncmp(arr1, arr2, 4);
    printf("%d\n", ret);
    return 0;
}

好了,今天的分享暂时告一段落,预知后续请看下篇,祝大家学习进步!