修改buffersize测试stdio的读写效率

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char **argv)
{
    if(argc < 2){
        fprintf(stderr, "faild Usage...\n");
        exit(1);
    }
    int buffersize = atoi(argv[1]);
    char buf[buffersize];
    int n = 0;
    while((n = read(STDIN_FILENO, buf, buffersize)) > 0){
        if(write(STDOUT_FILENO, buf, n) != n){
            perror("write()");
        }
    }

    if(n < 0){
        perror("read()");
    }
    exit(0);
}