write和fwrite
时间: 2024-05-17 20:08:49 浏览: 13
write和fwrite都是用于文件操作的函数,但在不同编程语言中有不同的实现方式。
在C语言中,write函数是一个系统调用,用于将数据从内存写入到文件中。它的原型如下:
```c
ssize_t write(int fd, const void *buf, size_t count);
```
其中,fd是文件描述符,buf是要写入的数据的指针,count是要写入的字节数。write函数返回实际写入的字节数,如果出错则返回-1。
而在C语言中,fwrite函数是标准库函数,用于将数据块写入到文件中。它的原型如下:
```c
size_t fwrite(const void *ptr, size_t size, size_t count, FILE *stream);
```
其中,ptr是要写入的数据块的指针,size是每个数据块的字节数,count是要写入的数据块的个数,stream是文件指针。fwrite函数返回实际写入的数据块个数,如果出错则返回0。
总结一下:
- write函数是系统调用,直接将数据从内存写入到文件中。
- fwrite函数是标准库函数,将数据块写入到文件中。
相关问题
fwrite demo
Sure, here is a simple demonstration of using the `fwrite` function in C:
```c
#include <stdio.h>
int main() {
FILE *fp;
char data[] = "Hello, CSDN!";
// Open file for writing
fp = fopen("output.txt", "w");
if (fp == NULL) {
printf("Failed to open file.\n");
return 1;
}
// Write data to file
fwrite(data, sizeof(char), sizeof(data) - 1, fp);
// Close file
fclose(fp);
printf("Data written to file.\n");
return 0;
}
```
In this example, we include the `stdio.h` library for file I/O operations. We declare a file pointer `fp` and a character array `data` containing the string we want to write to the file.
We open a file named "output.txt" in write mode using `fopen`. If the file fails to open, an error message is printed and the program returns. Otherwise, we use `fwrite` to write the contents of the `data` array to the file.
After writing the data, we close the file using `fclose`. Finally, a success message is printed.
fopen fwrite
`fopen` and `fwrite` are functions used in the C programming language to open a file and write data to it, respectively.
The `fopen` function is used to open a file and obtain a file pointer that can be used for subsequent file operations. Its syntax is:
```c
FILE *fopen(const char *filename, const char *mode);
```
Here, `filename` is a string that specifies the name of the file to be opened, and `mode` is a string that specifies the mode in which the file will be opened (e.g., `"r"` for reading, `"w"` for writing, `"a"` for appending). The return value of `fopen` is a pointer to a `FILE` object, which represents the opened file. If the file cannot be opened, `NULL` is returned.
The `fwrite` function is used to write data to a file. Its syntax is:
```c
size_t fwrite(const void *ptr, size_t size, size_t count, FILE *stream);
```
Here, `ptr` is a pointer to the memory block containing the data to be written, `size` specifies the size of each element to be written, `count` specifies the number of elements to be written, and `stream` is a pointer to a `FILE` object that represents the file being written to. The return value of `fwrite` is the total number of elements successfully written.
These functions are commonly used for file input/output operations in C. Let me know if you have any specific questions or if there's anything else I can assist you with!
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