fread(buf,1,1024,fp);
时间: 2023-10-09 15:15:48 浏览: 52
This line of code reads 1024 bytes of data from the file pointer "fp" and stores it in the memory location pointed to by "buf". The "1" argument specifies that each element being read is one byte in size. If the end of file is reached before 1024 bytes are read, the function will return the number of bytes actually read.
相关问题
用C语言编写文件复制程序。分别使用系统调用read (fd,buf,nbytes)、write(fd, buf,nbytes)和文件的库函数fread(buf,size,nitems,fp)、fwrite(buf,size,nitems,fp),编写一个文件复制程序。
使用系统调用read和write实现文件复制程序:
```c
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#define BUF_SIZE 1024
int main(int argc, char *argv[]) {
int source_fd, target_fd;
ssize_t nread;
char buf[BUF_SIZE];
if (argc != 3) {
fprintf(stderr, "Usage: %s source_file target_file\n", argv[0]);
return 1;
}
source_fd = open(argv[1], O_RDONLY);
if (source_fd == -1) {
perror("open");
return 1;
}
target_fd = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC, 0644);
if (target_fd == -1) {
perror("open");
return 1;
}
while ((nread = read(source_fd, buf, BUF_SIZE)) > 0) {
if (write(target_fd, buf, nread) != nread) {
perror("write");
return 1;
}
}
if (nread == -1) {
perror("read");
return 1;
}
if (close(source_fd) == -1) {
perror("close");
return 1;
}
if (close(target_fd) == -1) {
perror("close");
return 1;
}
return 0;
}
```
使用文件的库函数fread和fwrite实现文件复制程序:
```c
#include <stdio.h>
#define BUF_SIZE 1024
int main(int argc, char *argv[]) {
FILE *source_fp, *target_fp;
size_t nread;
char buf[BUF_SIZE];
if (argc != 3) {
fprintf(stderr, "Usage: %s source_file target_file\n", argv[0]);
return 1;
}
source_fp = fopen(argv[1], "rb");
if (source_fp == NULL) {
perror("fopen");
return 1;
}
target_fp = fopen(argv[2], "wb");
if (target_fp == NULL) {
perror("fopen");
return 1;
}
while ((nread = fread(buf, 1, BUF_SIZE, source_fp)) > 0) {
if (fwrite(buf, 1, nread, target_fp) != nread) {
perror("fwrite");
return 1;
}
}
if (ferror(source_fp)) {
perror("fread");
return 1;
}
if (fclose(source_fp) != 0) {
perror("fclose");
return 1;
}
if (fclose(target_fp) != 0) {
perror("fclose");
return 1;
}
return 0;
}
```
fread c语言实现
fread是C语言中的一个文件读取函数,其函数原型为:
```c
size_t fread(void *ptr, size_t size, size_t count, FILE *stream);
```
其中,ptr是指向存储读取数据的缓冲区的指针;size是每个数据块的字节数;count是要读取的数据块的数量;stream是指向FILE对象的指针,该对象指向要读取的文件。
fread函数的返回值是实际读取的数据块数量,如果返回值小于count,则可能是读取到了文件末尾或者发生了错误。
下面是一个使用fread函数读取二进制文件的例子:
```c
#include <stdio.h>
int main() {
FILE *fp = fopen("test.bin", "rb");
if (fp == NULL) {
printf("Failed to open file.\n");
return 1;
}
char buf[1024];
size_t n = fread(buf, sizeof(char), sizeof(buf), fp);
if (n == 0) {
printf("Failed to read file.\n");
fclose(fp);
return 1;
}
printf("Read %zu bytes from file.\n", n);
fclose(fp);
return 0;
}
```
该程序打开名为test.bin的二进制文件,读取其中的数据到buf缓冲区中,最多读取1024个字节。如果读取成功,则输出读取的字节数,否则输出错误信息。