C, it's related to opening the txt file.

Answer 1

Opening a txt-file in C language mainly involved the following aspects:

** 1. Headers **
The standard input and output library header file of the C language,`stbio.h`, is required. This header file contains the functions for file operations.

** 2. Open the file **
1. ** Function Usage **
- Use the `fopen` function to open the file. The prototype is `Files *fopen(const charb * file name, const charb *mode);`. `Filename` is the name of the TMT file to be opened (including the path and other information), and `mode` is the mode in which the file is opened.
- The most common open mode for reading a txt-file was `"r"`(read-only mode, the file must exist). For example,`Files *file;file = fopen("filename.txt',"r");` Filename.txt', where `Filename.txt', is the name of the txt-file to be opened.
- If you want to write, there are `"w`"(write mode, if the file exists, clear the content, if the file does not exist, create a new file),`""a`(add mode, if the file exists, add content at the end of the file, if the file does not exist, create a new file), and so on.
2. ** Wrong handling **
- The `fopen` function returns a pointer to the `Files` object. If opening the file fails, it returns `Null'. Therefore, after opening a file, you usually need to check if the return value is `Null'. If it is, it means that the file has failed to open. It may be because the file does not exist (in read-only mode) or the permission is insufficient. For example:
```c
FILE *file;
file = fopen("test.txt", "r");
if (file == NULL) {
//You can use the perror function to print error messages
perror("Error opening file");
return 1;
}
```

** 3. Read the contents of the file (using the read-only mode as an example)**
1. ** Function Usage **
- You can use the `fgets` function to read the file contents line by line. The first argument of the fgets`function is an array of characters, which is used to store the contents to be read; the second argument is the maximum number of characters to be read; and the third argument is the file pointer. For example:
```c
char line[100];
while (fgets(line, sizeof(line), file)) {
//You can process the contents of each line here, for example, print it out.
printf("%s", line);
}
```
2. ** Cyclic Reading **
- Usually, the `while` loop is used in combination with the `fgets` function to read the contents of the file until the end of the file.

** 4. Close the file **
1. ** Function Usage **
- Use the `fclose` function to close the file. The prototype is `int fclose(Files *stream);`. After closing the file, there should be no more operations on the file.
- For example,`fclose(file);`.
2. ** Wrong handling **
- The `fclose` function returns 0 to indicate that the file has been successfully closed, and the `END`(usually-1) is returned to indicate that the file has failed to close. If it fails, it may be due to a file system error or a program anomaly.
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