c语言string.h中常用的字符串操作函数

//根据指定字符切分字符串char *strtok(char *str1, char *str2);
char input[26] = "I,am,a,boy";
char *p;
p = strtok(input, ",");
while(p)
{
	printf("%s
", p);
	p = strtok(NULL, ",");
}

//字符串反转char *strrev(char *str);
char forward[] = "string";
printf("Before strrev(): %s
", forward);
strrev(forward);
printf("After strrev(): %s
", forward);


//字符串中大小写转换，小写变大写：char *strupr(char *str);大写变小写：char *strlwr(char *str);
char str[30] = "abcdefghijklmnopqrstuvwxyz";
strupr(str);
printf(str);
strlwr(str);
printf(str);


//在一个串中查找给定字符的第一个匹配之处char *strchr(char *str, char c);
char str[22]="This is a string";
char* ptr=strchr(str, "i");
if (ptr)
   printf(ptr);
   
//在一个串中查找给定字符的最后一个匹配之处char *strrchr(char *str, char c);
char str[22]="This is a string";
char* ptr=strrchr(str, "i");
if (ptr)
   printf(ptr);
   
  
//在串中查找指定字符串的第一次出现char *strstr(char *str1, char *str2);
char str[22]="This is a string";
char* ptr=strstr(str,"is");
if (ptr)
  printf(ptr);
  
  
//将字符串转换为double型值double strtod(char *str, char **endptr);
//提取字符串中的小数
char str[52]="string89.23string0.896string4.56string";
char* ptr=str;
int i=0;
double nums[100];
while(*ptr!=0)
{
	if(*ptr>="0" && *ptr<="9")
		nums[i++]=strtod(ptr,&ptr);
	ptr++;
}
for(int j=0;j="0" && *ptr<="9")
		nums[i++]=strtol(ptr,&ptr,10);
	ptr++;
}
for(int j=0;j