string.h

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1、c++中 string 与 string.h 的作用和区别答：一般一个 C++的老的带“.h”扩展名的库文件，比如 iostream.h，在新标准后的标准库中都有一个不带“.h”扩展名的相对应，区别除了后者的好多改进之外，还有一点就是后者的东东都塞进了“std”名字空间中。但唯独 string 特别。问题在于 C++要兼容 C 的标准库，而 C 的标准库里碰巧也已经有一个名字叫做“string.h”的头文件，包含一些常用的 C 字符串处理函数。这个头文件跟 C++的 string 类半点关系也没有，所以 <string>并非 <string.h>的“升级版本”，他们是毫无关系的两个头文件。
2、c++ <string.h>中包括哪些函数？答：常用函数如下： strlen 求字符串长度 strcmp 比较 2 个字符串是否一样 strcat 字符串连接操作 strcpy 字符串拷贝操作 strstr 查询子串
下面为 string.h 文件中函数的详细用法，附加实例：
1、strcpy 函数名: strcpy 功能: 拷贝一个字符串到另一个用法: char *strcpy(char *destin, char *source); 程序例: #include <stdio.h> #include <string.h> int main(void) { char string[10]; char *str1 = "abcdefghi"; strcpy(string, str1); printf("%s\n", string); return 0; }
2、strcat 函数名: strcat 功能: 字符串拼接函数用法: char *strcat(char *destin, char *source); 程序例: #include <string.h> #include <stdio.h> int main(void)
{ char destination[25]; char *blank = " ", *c = "C++", *Borland = "Borland"; strcpy(destination, Borland); strcat(destination, blank); strcat(destination, c); printf("%s\n", destination); return 0; }
3、strchr 函数名: strchr 功能: 在一个串中查找给定字符的第一个匹配之处\ 用法: char *strchr(char *str, char c); 程序例: #include <string.h> #include <stdio.h> int main(void) { char string[15]; char *ptr, c = 'r'; strcpy(string, "This is a string"); ptr = strchr(string, c); if (ptr) printf("The character %c is at position: %d\n", c, ptr-string); else printf("The character was not found\n"); return 0; }
4、strcmp 函数名: strcmp 功能: 串比较用法: int strcmp(char *str1, char *str2); 看 Asic 码，str1>str2，返回值 > 0；两串相等，返回 0 程序例: #include <string.h> #include <stdio.h> int main(void) { char *buf1 = "aaa", *buf2 = "bbb", *buf3 = "ccc"; int ptr; ptr = strcmp(buf2, buf1); if (ptr > 0) printf("buffer 2 is greater than buffer 1\n");
else printf("buffer 2 is less than buffer 1\n"); ptr = strcmp(buf2, buf3); if (ptr > 0) printf("buffer 2 is greater than buffer 3\n"); else printf("buffer 2 is less than buffer 3\n"); return 0; }
5、strncmpi 函数名: strncmpi 功能: 将一个串中的一部分与另一个串比较, 不管大小写用法: int strncmpi(char *str1, char *str2, unsigned maxlen); 程序例: #include <string.h> #include <stdio.h> int main(void) { char *buf1 = "BBB", *buf2 = "bbb"; int ptr; ptr = strcmpi(buf2, buf1); if (ptr > 0) printf("buffer 2 is greater than buffer 1\n"); if (ptr < 0) printf("buffer 2 is less than buffer 1\n"); if (ptr == 0) printf("buffer 2 equals buffer 1\n"); return 0; }
6、strcpy 函数名: strcpy 功能: 串拷贝用法: char *strcpy(char *str1, char *str2); 程序例: #include <stdio.h> #include <string.h> int main(void) { char string[10]; char *str1 = "abcdefghi"; strcpy(string, str1); printf("%s\n", string); return 0;
}
7、strcspn 函数名: strcspn 功能: 在串中查找第一个给定字符集内容的段用法: int strcspn(char *str1, char *str2); 程序例: #include <stdio.h> #include <string.h> #include <alloc.h> int main(void) { char *string1 = "1234567890"; char *string2 = "747DC8"; int length; length = strcspn(string1, string2); printf("Character where strings intersect is at position %d\n", length); return 0; }
8、strdup 函数名: strdup 功能: 将串拷贝到新建的位置处用法: char *strdup(char *str); 程序例: #include <stdio.h> #include <string.h> #include <alloc.h> int main(void) { char *dup_str, *string = "abcde"; dup_str = strdup(string); printf("%s\n", dup_str); free(dup_str); return 0; }
9、stricmp 函数名: stricmp 功能: 以大小写不敏感方式比较两个串用法: int stricmp(char *str1, char *str2); 程序例: #include <string.h> #include <stdio.h> int main(void)
{ char *buf1 = "BBB", *buf2 = "bbb"; int ptr; ptr = stricmp(buf2, buf1); if (ptr > 0) printf("buffer 2 is greater than buffer 1\n"); if (ptr < 0) printf("buffer 2 is less than buffer 1\n"); if (ptr == 0) printf("buffer 2 equals buffer 1\n"); return 0; }
10、strerror 函数名: strerror 功能: 返回指向错误信息字符串的指针用法: char *strerror(int errnum); 程序例: #include <stdio.h> #include <errno.h> int main(void) { char *buffer; buffer = strerror(errno); printf("Error: %s\n", buffer); return 0; }
11、strcmpi 函数名: strcmpi 功能: 将一个串与另一个比较, 不管大小写用法: int strcmpi(char *str1, char *str2); 程序例: #include <string.h> #include <stdio.h> int main(void) { char *buf1 = "BBB", *buf2 = "bbb"; int ptr; ptr = strcmpi(buf2, buf1); if (ptr > 0) printf("buffer 2 is greater than buffer 1\n"); if (ptr < 0) printf("buffer 2 is less than buffer 1\n"); if (ptr == 0)
printf("buffer 2 equals buffer 1\n"); return 0; } 函数名: strncmp 功能: 串比较用法: int strncmp(char *str1, char *str2, int maxlen); 程序例: #include <string.h> #include <stdio.h> int main(void) { char *buf1 = "aaabbb", *buf2 = "bbbccc", *buf3 = "ccc"; int ptr; ptr = strncmp(buf2,buf1,3); if (ptr > 0) printf("buffer 2 is greater than buffer 1\n"); else printf("buffer 2 is less than buffer 1\n"); ptr = strncmp(buf2,buf3,3); if (ptr > 0) printf("buffer 2 is greater than buffer 3\n"); else printf("buffer 2 is less than buffer 3\n"); return(0); }
12、strncpy 函数名: strncpy 功能: 串拷贝用法: char *strncpy(char *destin, char *source, int maxlen); 程序例: #include <stdio.h> #include <string.h> int main(void) { char string[10]; char *str1 = "abcdefghi"; strncpy(string, str1, 3); string[3] = '\0'; printf("%s\n", string); return 0; }
13、strnicmp 函数名: strnicmp
功能: 不注重大小写地比较两个串用法: int strnicmp(char *str1, char *str2, unsigned maxlen); 程序例: #include <string.h> #include <stdio.h> int main(void) { char *buf1 = "BBBccc", *buf2 = "bbbccc"; int ptr; ptr = strnicmp(buf2, buf1, 3); if (ptr > 0) printf("buffer 2 is greater than buffer 1\n"); if (ptr < 0) printf("buffer 2 is less than buffer 1\n"); if (ptr == 0) printf("buffer 2 equals buffer 1\n"); return 0; }
14、strnset 函数名: strnset 功能: 将一个字符串前 n 个字符都设为指定字符用法: char *strnset(char *str, char ch, unsigned n); 程序例: #include <stdio.h> #include <string.h> int main(void) { char *string = "abcdefghijklmnopqrstuvwxyz"; char letter = 'x'; printf("string before strnset: %s\n", string); strnset(string, letter, 13); printf("string after strnset: %s\n", string); return 0; }
15、strpbrk 函数名: strpbrk 功能: 在串中查找给定字符集中的字符用法: char *strpbrk(char *str1, char *str2); 程序例: #include <stdio.h> #include <string.h> int main(void) {
char *string1 = "abcdefghijklmnopqrstuvwxyz"; char *string2 = "onm"; char *ptr; ptr = strpbrk(string1, string2); if (ptr) printf("strpbrk found first character: %c\n", *ptr); else printf("strpbrk didn't find character in set\n"); return 0; }
16、strrchr 函数名: strrchr 功能: 在串中查找指定字符的最后一个出现用法: char *strrchr(char *str, char c); 程序例: #include <string.h> #include <stdio.h> int main(void) { char string[15]; char *ptr, c = 'r'; strcpy(string, "This is a string"); ptr = strrchr(string, c); if (ptr) printf("The character %c is at position: %d\n", c, ptr-string); else printf("The character was not found\n"); return 0; }
17、strrev 函数名: strrev 功能: 串倒转用法: char *strrev(char *str); 程序例: #include <string.h> #include <stdio.h> int main(void) { char *forward = "string"; printf("Before strrev(): %s\n", forward); strrev(forward); printf("After strrev(): %s\n", forward); return 0;
}
18、strset 函数名: strset 功能: 将一个串中的所有字符都设为指定字符用法: char *strset(char *str, char c); 程序例: #include <stdio.h> #include <string.h> int main(void) { char string[10] = "123456789"; char symbol = 'c'; printf("Before strset(): %s\n", string); strset(string, symbol); printf("After strset(): %s\n", string); return 0; }
19、strspn 函数名: strspn 功能: 在串中查找指定字符集的子集的第一次出现用法: int strspn(char *str1, char *str2); 程序例: #include <stdio.h> #include <string.h> #include <alloc.h> int main(void) { char *string1 = "1234567890"; char *string2 = "123DC8"; int length; length = strspn(string1, string2); printf("Character where strings differ is at position %d\n", length); return 0; }
20、strstr 函数名: strstr 功能: 在串中查找指定字符串的第一次出现用法: char *strstr(char *str1, char *str2); 程序例: #include <stdio.h> #include <string.h> int main(void)
{ char *str1 = "Borland International", *str2 = "nation", *ptr; ptr = strstr(str1, str2); printf("The substring is: %s\n", ptr); return 0; }
21、strtod 函数名: strtod 功能: 将字符串转换为 double 型值用法: double strtod(char *str, char **endptr); 程序例: #include <stdio.h> #include <stdlib.h> int main(void) { char input[80], *endptr; double value; printf("Enter a floating point number:"); gets(input); value = strtod(input, &endptr); printf("The string is %s the number is %lf\n", input, value); return 0; }
22、strtok 函数名: strtok 功能: 查找由在第二个串中指定的分界符分隔开的单词用法: char *strtok(char *str1, char *str2); 程序例: #include <string.h> #include <stdio.h> int main(void) { char input[16] = "abc,d"; char *p; /* strtok places a NULL terminator in front of the token, if found */ p = strtok(input, ","); if (p) printf("%s\n", p); /* A second call to strtok using a NULL as the first parameter returns a pointer to the character following the token */ p = strtok(NULL, ","); if (p) printf("%s\n", p);
return 0; }
23、strtol 函数名: strtol 功能: 将串转换为长整数用法: long strtol(char *str, char **endptr, int base); 程序例: #include <stdlib.h> #include <stdio.h> int main(void) { char *string = "87654321", *endptr; long lnumber; /* strtol converts string to long integer */ lnumber = strtol(string, &endptr, 10); printf("string = %s long = %ld\n", string, lnumber); return 0; }
24、strupr 函数名: strupr 功能: 将串中的小写字母转换为大写字母用法: char *strupr(char *str); 程序例: #include <stdio.h> #include <string.h> int main(void) { char *string = "abcdefghijklmnopqrstuvwxyz", *ptr; /* converts string to upper case characters */ ptr = strupr(string); printf("%s\n", ptr); return 0; }
25、swab 函数名: swab 功能: 交换字节用法: void swab (char *from, char *to, int nbytes); 程序例: #include <stdlib.h> #include <stdio.h> #include <string.h> char source[15] = "rFna koBlrna d"; char target[15];
int main(void) { swab(source, target, strlen(source)); printf("This is target: %s\n", target); return 0; 原型：extern char *strstr(char *haystack, char *needle); *所在头文件：#include <string.h> *功能：从字符串 haystack 中寻找 needle 第一次出现的位置（不比较结束符 NULL)。 *说明：返回指向第一次出现 needle位置的指针，如果没找到则返回 NULL。

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