C标准I/O操作

//打印默认打开的流的文件描述符
#include<stdio.h>

int main()
{

    printf("%d\t",stdin->_fileno);
    printf("%d\t",stdout->_fileno);
    printf("%d\n",stderr->_fileno);

}


//测试一个进程能打开的文件描述符的最大值
#include<stdio.h>

int main()
{
    int n = 3;
    FILE *p;
    while((p = fopen("fileno.c","r")) != NULL)
    {
        n++;
    }
    printf("number:%d\n", n);
    return 0;
}

//按字节复制文件
int c;
while((c=fgetc(in_fp))!= EOF)
{
      fputc(c,out_fp);
}


//按行复制文件
  while(fgets(buf, BUFFERSIZE, in_fp) != NULL)
 {
        fputs(buf, out_fp);
 }


//计算文件中的行数
if(buf[strlen(buf)-1] == '\n') count++;


//按指定大小读写一个流
while((n = fread(buf, 1, 128, in_fp))>0)
{   
      fwrite(buf, 1, n, out_fp);
}



//按字节复制文件实例
#include<stdio.h>
#include<stdlib.h>

int main(int argc, char *argv[])
{
    FILE *in_fp, *out_fp;
    char c;
    if(argc < 3)
    {
        fprintf(stderr,"usage:%s source destination\n", argv[0]);
        exit(1);
    }

    if((in_fp = fopen(argv[1],"r")) == NULL)
    {
        fprintf(stderr, "can't open %s", argv[1]);
        perror(argv[1]);
        exit(1);
    }

    if((out_fp = fopen(argv[2],"w+")) == NULL)
    {
        fprintf(stderr,"can't open %s", argv[2]);
        perror(argv[2]);
        exit(1);
    }

    while((c=fgetc(in_fp))!= EOF)
    {
        fputc(c,out_fp);
    }

    if(fclose(in_fp)==-1 || fclose(out_fp)==-1)
    {
        fprintf(stderr,"can't close");
        perror("");
        exit(1);
    }
    return 0;
}

//错误输出
#include <string.h>
#include <errno.h>
printf("fail to fopen %s : %s\n", argv[2], strerror(errno));


fprintf(stderr,"can't open");
perror(argv[2]);//打印默认打开的流的文件描述符
#include<stdio.h>

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