void exchg(char * str)
{
if(str == NULL) return;
int len = strlen(str);
char tmp;
for(int i=0,j=len-1;i<j;)
{
tmp = str[i];
str[i++] = str[j];
str[j--] = tmp;
}
}原文：https://www.cnblogs.com/wjundong/p/11556099.html