文章目录
- 二、字符串的输入
- 3.gets()的替代品
- （1）fgets()与gets()的区别
- （2）空字符和空指针的区别
- 五、字符串函数
- 1.strlen()函数：统计字符串的长度
- 2.strcat()函数：拼接字符串
- 3.strncat()函数：更安全
- 4.strcmp()函数：持续到字符串的尾巴
- （1）字符串不能比较地址，只能比较字符串的内容
- （2）不要使用字符或者'a'来作为strcmp()的参数
- 二维数组如何检测输入空行？
- 5.strncmp()函数：可以比较字符串不同地方
- 指针数组的运用!!
- 6.strcpy()函数
- 二维数组与字符串的结合使用！！
- 字符指针的运用
- 7.strncpy()函数：更安全
- 同样使用二维数组，来操作字符串
- 8.sprintf()函数
- 9.常用字符串函数用法大总结
二、字符串的输入
3.gets()的替代品
（1）fgets()与gets()的区别
eg：
/* fgets1.c -- using fgets() and fputs() */
#include <stdio.h>
#define STLEN 14
int main(void)
{
char words[STLEN];
puts("Enter a string, please.");
fgets(words, STLEN, stdin);
printf("Your string twice (puts(), then fputs()):\n");
puts(words);
fputs(words, stdout);
puts("Enter another string, please.");
fgets(words, STLEN, stdin);
printf("Your string twice (puts(), then fputs()):\n");
puts(words);
fputs(words, stdout);
puts("Done.");
return 0;
}
解释如下：
eg：这是一个简单的循环，读入并显示用户输入的内容，直到fgets()读到文件结尾或空行 （即，首字符是换行符）
#include<iostream>
using namespace std;
/* fgets2.c -- using fgets() and fputs() */
#include <stdio.h>
#define STLEN 10
int main(void)
{
char words[STLEN];
puts("Enter strings (empty line to quit):");
while (fgets(words, STLEN, stdin) != NULL && words[0] != '\n')
fputs(words, stdout);
puts("Done.");
cin.get();
return 0;
}
解释如下：
eg：在上面的例子基础上增加了代码，改程序读取输入行，删除存储存在字符串中的换行符，如果没有换行符，就丢弃数组装不下的字符。
/* fgets3.c -- using fgets() */
#include <stdio.h>
#define STLEN 10
int main(void)
{
char words[STLEN];
int i;
puts("Enter strings (empty line to quit):");
while (fgets(words, STLEN, stdin) != NULL
&& words[0] != '\n')
{
i = 0;
while (words[i] != '\n' && words[i] != '\0')
i++;
if (words[i] == '\n')
words[i] = '\0';
else // must have words[i] == '\0'
while (getchar() != '\n')
continue;
puts(words);
}
puts("done");
return 0;
}
解释如下：
（2）空字符和空指针的区别
五、字符串函数
1.strlen()函数：统计字符串的长度
（1）eg：
/* test_fit.c -- try the string-shrinking function */
#include <stdio.h>
#include <string.h> /* contains string function prototypes */
void fit(char *, unsigned int);
int main(void)
{
char mesg[] = "Things should be as simple as possible,"
" but not simpler.";
puts(mesg);
fit(mesg,38);
puts(mesg);
puts("Let's look at some more of the string.");
puts(mesg + 39);
return 0;
}
void fit(char *string, unsigned int size)
{
if (strlen(string) > size)
string[size] = '\0';
}
解释：
（2）其他eg
2.strcat()函数：拼接字符串
（1）strcat()函数说明
（2）代码如下
/* str_cat.c -- joins two strings */
#include <stdio.h>
#include <string.h> /* declares the strcat() function */
#define SIZE 80
char * s_gets(char * st, int n);
int main(void)
{
char flower[SIZE];
char addon[] = "s smell like old shoes.";
puts("What is your favorite flower?");
if (s_gets(flower, SIZE))
{
strcat(flower, addon);
puts(flower);
puts(addon);
}
else
puts("End of file encountered!");
puts("bye");
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);//fgets()读取整行，包括换行符
if (ret_val)
{
while (st[i] != '\n' && st[i] != '\0')//把换行符换成空字符\0
i++;
if (st[i] == '\n')
st[i] = '\0';
else // must have words[i] == '\0'、、抛弃>=n的字符
while (getchar() != '\n')
continue;
}
return ret_val;
}
3.strncat()函数：更安全
（1）strncat()函数解释
（2）eg：计算avaiable变量的值，用于表示允许添加的最大字符数
/* join_chk.c -- joins two strings, check size first */
#include <stdio.h>
#include <string.h>
#define SIZE 30
#define BUGSIZE 13
char * s_gets(char * st, int n);
int main(void)
{
char flower[SIZE];
char addon[] = "s smell like old shoes.";
char bug[BUGSIZE];
int available;
puts("What is your favorite flower?");
s_gets(flower, SIZE);
if ((strlen(addon) + strlen(flower) + 1) <= SIZE)
strcat(flower, addon);
puts(flower);
puts("What is your favorite bug?");
s_gets(bug, BUGSIZE);
available = BUGSIZE - strlen(bug) - 1;//13-5-1=7
strncat(bug, addon, available);
puts(bug);
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else // must have words[i] == '\0'
while (getchar() != '\n')
continue;
}
return ret_val;
}
4.strcmp()函数：持续到字符串的尾巴
（1）字符串不能比较地址，只能比较字符串的内容
错误程序如下：
/* nogo.c -- will this work? */
#include <stdio.h>
#define ANSWER "Grant"
#define SIZE 40
char * s_gets(char * st, int n);
int main(void)
{
char try[SIZE];
puts("Who is buried in Grant's tomb?");
s_gets(try, SIZE);
while (try != ANSWER)
{
puts("No, that's wrong. Try again.");
s_gets(try, SIZE);
}
puts("That's right!");
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else // must have words[i] == '\0'
while (getchar() != '\n')
continue;
}
return ret_val;
}
正确的程序如下：
/* compare.c -- this will work */
#include <stdio.h>
#include <string.h> // declares strcmp()
#define ANSWER "Grant"
#define SIZE 40
char * s_gets(char * st, int n);
int main(void)
{
char try[SIZE];
puts("Who is buried in Grant's tomb?");
s_gets(try, SIZE);
while (strcmp(try,ANSWER) != 0)
{
puts("No, that's wrong. Try again.");
s_gets(try, SIZE);
}
puts("That's right!");
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else // must have words[i] == '\0'
while (getchar() != '\n')
continue;
}
return ret_val;
}
（2）不要使用字符或者’a’来作为strcmp()的参数
eg：
/* quit_chk.c -- beginning of some program */
#include <stdio.h>
#include <string.h>
#define SIZE 80
#define LIM 10
#define STOP "quit"
char * s_gets(char * st, int n);
int main(void)
{
char input[LIM][SIZE];
int ct = 0;
printf("Enter up to %d lines (type quit to quit):\n", LIM);
while (ct < LIM && s_gets(input[ct], SIZE) != NULL &&
strcmp(input[ct],STOP) != 0)
{
ct++;
}
printf("%d strings entered\n", ct);
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else // must have words[i] == '\0'
while (getchar() != '\n')
continue;
}
return ret_val;
}
解释如下：
二维数组如何检测输入空行？
5.strncmp()函数：可以比较字符串不同地方
指针数组的运用!!
（1）eg：要查找以“”astro“开头的字符串，可以限定函数只查找这5个字符串
/* starsrch.c -- use strncmp() */
#include <stdio.h>
#include <string.h>
#define LISTSIZE 6
int main()
{
const char * list[LISTSIZE] =
{
"astronomy", "astounding",//有6个指针，指向不同的字符串
"astrophysics", "ostracize",
"asterism", "astrophobia"
};
int count = 0;
int i;
for (i = 0; i < LISTSIZE; i++)
if (strncmp(list[i],"astro", 5) == 0)
{
printf("Found: %s\n", list[i]);
count++;
}
printf("The list contained %d words beginning"
" with astro.\n", count);
return 0;
}
6.strcpy()函数
二维数组与字符串的结合使用！！
（1）strcpy()函数相当于字符串赋值运算符
/* copy1.c -- strcpy() demo */
#include <stdio.h>
#include <string.h> // declares strcpy()
#define SIZE 40
#define LIM 5
char * s_gets(char * st, int n);
int main(void)
{
char qwords[LIM][SIZE];
char temp[SIZE];
int i = 0;
printf("Enter %d words beginning with q:\n", LIM);
while (i < LIM && s_gets(temp, SIZE))
{
if (temp[0] != 'q')
printf("%s doesn't begin with q!\n", temp);
else
{
strcpy(qwords[i], temp);
i++;
}
}
puts("Here are the words accepted:");
for (i = 0; i < LIM; i++)
puts(qwords[i]);
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else // must have words[i] == '\0'
while (getchar() != '\n')
continue;
}
return ret_val;
}
（2）strcpy()函数的其他属性
- strcpy()的返回类型是char *，该函数返回的是第1个参数的值，即一个字符的地址；
- 第1个参数不必指向数组的开始；
字符指针的运用
eg：
/* copy2.c -- strcpy() demo */
#include <stdio.h>
#include <string.h> // declares strcpy()
#define WORDS "beast"
#define SIZE 40
int main(void)
{
const char * orig = WORDS;
char copy[SIZE] = "Be the best that you can be.";
char * ps;
puts(orig);
puts(copy);
ps = strcpy(copy + 7, orig);
puts(copy);
puts(ps);
return 0;
}
解释：
7.strncpy()函数：更安全
同样使用二维数组，来操作字符串
（1）
/* copy3.c -- strncpy() demo */
#include <stdio.h>
#include <string.h> /* declares strncpy() */
#define SIZE 40
#define TARGSIZE 7
#define LIM 5
char * s_gets(char * st, int n);
int main(void)
{
char qwords[LIM][TARGSIZE];
char temp[SIZE];
int i = 0;
printf("Enter %d words beginning with q:\n", LIM);
while (i < LIM && s_gets(temp, SIZE))
{
if (temp[0] != 'q')
printf("%s doesn't begin with q!\n", temp);
else
{
strncpy(qwords[i], temp, TARGSIZE - 1);
qwords[i][TARGSIZE - 1] = '\0';
i++;
}
}
puts("Here are the words accepted:");
for (i = 0; i < LIM; i++)
puts(qwords[i]);
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else // must have words[i] == '\0'
while (getchar() != '\n')
continue;
}
return ret_val;
}
8.sprintf()函数
（1）sprintf()的功能
（2）eg，程序说明如下：
/* format.c -- format a string */
#include <stdio.h>
#define MAX 20
char * s_gets(char * st, int n);
int main(void)
{
char first[MAX];
char last[MAX];
char formal[2 * MAX + 10];
double prize;
puts("Enter your first name:");
s_gets(first, MAX);
puts("Enter your last name:");
s_gets(last, MAX);
puts("Enter your prize money:");
scanf("%lf", &prize);
sprintf(formal, "%s, %-19s: $%6.2f\n", last, first, prize);
puts(formal);
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else // must have words[i] == '\0'
while (getchar() != '\n')
continue;
}
return ret_val;
}
9.常用字符串函数用法大总结
