字符串函数是最问常用的库函数之一，本文整理了常用的字符串函数，其来源为互联网

函数名: stpcpy

功 能: 拷贝一个字符串到另一个
用 法: char *stpcpy(char *destin, char *source);
程序例:

#include <stdio.h>
#include <string.h>
int main(void)
{char string[10];char *str1 = "abcdefghi";stpcpy(string, str1);printf("%sn", string);return 0;
}

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("%sn", destination);return 0;
}

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: %dn", c, ptr-string);elseprintf("The character was not foundn");return 0;}

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 1n"); else printf("buffer 2 is less than buffer 1n"); ptr = strcmp(buf2, buf3); if (ptr > 0) printf("buffer 2 is greater than buffer 3n"); else printf("buffer 2 is less than buffer 3n"); return 0; }

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 1n"); if (ptr < 0) printf("buffer 2 is less than buffer 1n"); if (ptr == 0) printf("buffer 2 equals buffer 1n"); return 0;
}

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("%sn", string); return 0;
}

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 %dn", length); return 0;
}

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("%sn", dup_str); free(dup_str); return 0;
}

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 1n"); if (ptr < 0) printf("buffer 2 is less than buffer 1n"); if (ptr == 0) printf("buffer 2 equals buffer 1n"); return 0;
}

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: %sn", buffer); return 0;
}

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 1n"); if (ptr < 0) printf("buffer 2 is less than buffer 1n"); if (ptr == 0) printf("buffer 2 equals buffer 1n"); 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 1n"); else printf("buffer 2 is less than buffer 1n"); ptr = strncmp(buf2,buf3,3); if (ptr > 0) printf("buffer 2 is greater than buffer 3n"); else printf("buffer 2 is less than buffer 3n"); return(0);
}

函数名: strncmpi

功 能: 把串中的一部分与另一串中的一部分比较, 不管大小写
用 法: int strncmpi(char *str1, char *str2);
程序例:

#include <string.h>
#include <stdio.h>
int main(void)
{ char *buf1 = "BBBccc", *buf2 = "bbbccc"; int ptr; ptr = strncmpi(buf2,buf1,3); if (ptr > 0) printf("buffer 2 is greater than buffer 1n"); if (ptr < 0) printf("buffer 2 is less than buffer 1n"); if (ptr == 0) printf("buffer 2 equals buffer 1n"); return 0;
}

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] = ''; printf("%sn", string); return 0;
}

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 1n"); if (ptr < 0) printf("buffer 2 is less than buffer 1n"); if (ptr == 0) printf("buffer 2 equals buffer 1n"); return 0;
}

函数名: strnset

功 能: 将一个串中的所有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: %sn", string); strnset(string, letter, 13); printf("string after  strnset: %sn", string); return 0;
}

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: %cn", *ptr); else printf("strpbrk didn't find character in setn"); return 0;
}

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: %dn", c, ptr-string); else printf("The character was not foundn"); return 0;
}

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(): %sn", forward); strrev(forward); printf("After strrev():  %sn", forward); return 0;
}

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(): %sn", string); strset(string, symbol); printf("After strset():  %sn", string); return 0;
}

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 %dn", length); return 0;
}

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: %sn", ptr); return 0;
}

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 %lfn", input, value); return 0;
}

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("%sn", 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("%sn", p); return 0;
}

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 = %ldn", string, lnumber); return 0;
}

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("%sn", ptr); return 0;
}

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: %sn", target); return 0;
}

isalpha()

PS:isalpha()是字符函数，不是字符串函数
原型：extern int isalpha(int c);
用法：#include <ctype.h>
功能：判断字符c是否为英文字母
说明：当c为英文字母a-z或A-Z时，返回非零值，否则返回零。
举例：

#include <syslib.h>
#include <ctype.h>
#include <stdio.h>main()
{int c;clrscr();        // clear screenprintf("Press a key");for(;;){c=getchar();clrscr();printf("%c: %s letter",c,isalpha(c)?"is":"not");}return 0; // just to avoid warnings by compiler
}