fopen(fileName,"a");
时间: 2024-05-19 14:13:15 浏览: 8
This line of code opens a file named "fileName" in append mode.
The "a" in the second argument of the fopen function stands for "append". This means that any data written to the file will be added to the end of the existing data, rather than overwriting it.
If the file does not already exist, it will be created.
相关问题
fid = fopen(filename,'r')
As an AI language model, I do not have access to the local file system. However, I can explain the syntax of the given code.
The code `fid = fopen(filename,'r')` is used to open a file in read-only mode. `filename` is a string that specifies the name of the file to be opened. `fid` is a file identifier that is returned by the `fopen` function. This identifier is used in subsequent file operations to refer to the opened file.
If the file could not be opened, `fopen` returns -1. Otherwise, it returns a positive integer value, which is the file identifier.
Example:
Suppose we have a file named `test.txt` in the current working directory. We can open the file in read-only mode using the following code:
```
fid = fopen('test.txt', 'r');
```
This code will return a file identifier `fid`, which can be used to perform file operations such as reading data from the file.
fp = fopen(filename, "r");和fp = fopen(filename, "w");的区别举例
`fp = fopen(filename, "r");` 打开文件用于读取。
例如,如果有一个名为 `data.txt` 的文本文件,它包含一些数据,可以使用以下代码读取文件:
```c
FILE* fp = fopen("data.txt", "r");
if (fp == NULL) {
fprintf(stderr, "Error opening file\n");
exit(1);
}
int num;
fscanf(fp, "%d", &num);
printf("Read number %d from file\n", num);
fclose(fp);
```
这个代码片段会打开一个名为 `data.txt` 的文件,然后读取文件中的一个整数。如果文件无法打开,会输出错误信息并退出程序。
`fp = fopen(filename, "w");` 打开文件用于写入。
例如,可以使用以下代码向一个名为 `output.txt` 的文本文件写入一些数据:
```c
FILE* fp = fopen("output.txt", "w");
if (fp == NULL) {
fprintf(stderr, "Error opening file\n");
exit(1);
}
fprintf(fp, "Hello, world!\n");
fprintf(fp, "The answer is %d\n", 42);
fclose(fp);
```
这个代码片段会打开一个名为 `output.txt` 的文件,然后向文件中写入两行数据。如果文件无法打开,会输出错误信息并退出程序。
需要注意的是,如果文件已经存在,`fopen(filename, "w");` 会清空文件中的所有内容并写入新的数据。如果不想清空文件,可以使用 `fopen(filename, "a");` 打开文件以追加数据。
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