C Operation of language files

Document classification ： text file 、 Binary

Open file fopen( Path and file name , Turn on mode )

If it is opened successfully, it will return to FILE Pointer to structure , Otherwise return to null Fixed error
Because the system newline character is the same as C Different language , So we should distinguish between text files and binary files , Only Unix Is with the C The language is the same , There is no need to distinguish between file types .
1.“r” Pattern ：

          1.1  Open the file for “ read-only ” operation , That is, you can only read content from files .

          1.2  If the file you want to operate does not exist , Open failed .

          1.3  When the file is successfully opened , The file pointer is at the beginning of the file .

          1.4  After opening the file , The original contents in the file will not be emptied .

          1.5  The content can be read from anywhere in the file .

   2."w"  Pattern ：

          2.1  Open the file for “ Just write ” operation , That is, only the contents can be written to the file .

          2.2  If the file you want to operate does not exist , Create a new file .

          2.3  When the file is successfully opened , The file pointer is at the beginning of the file .

          2.4  After opening the file , The original contents in the file will be emptied .

          2.5  You can write content anywhere in the file , And when writing , It will overwrite the contents of the original location .

   3."a"  Pattern ：

          3.1  Open the file for “ Additional ” operation , That is, only the contents can be written to the file .

          3.2  If the file you want to operate does not exist , Create a new file .

          3.3  When the file is successfully opened , The file pointer is at the end of the file .

          3.4  After opening the file , The original contents in the file will not be emptied .

          3.5  Can only be appended to the end of the file ( Write ) Content .

   4."r+" Pattern ：

          4.1  Open the file for “ Reading and writing ” operation , That is, it can be read , Write again .

          4.2  If the file you want to operate does not exist , Open failed .

          4.3  When the file is successfully opened , The file pointer is at the beginning of the file .

          4.4  After opening the file , The original contents in the file will not be emptied .

          4.5  Whether reading or writing content , Can be done anywhere in the file , And when writing , It will overwrite the contents of the original location .

   5."w+" Pattern ：

          5.1  Open the file for “ Reading and writing ” operation , That is, it can be read , Write again .

          5.2  If the file you want to operate does not exist , Create a new file .

          5.3  When the file is successfully opened , The file pointer is at the beginning of the file .

          5.4  After opening the file , The original contents in the file will be emptied .

          5.5  Whether reading or writing content , Can be done anywhere in the file , And when writing , It will overwrite the contents of the original location .

   6."a+" Pattern ：

          6.1  Open the file for “ Reading and writing ” operation , That is, it can be read , Write again .

          6.2  If the file you want to operate does not exist , Create a new file .

          6.3  When the file is successfully opened , The file pointer is at the end of the file .

          6.4  After opening the file , The original contents in the file will not be emptied .

          6.5  When reading content , It can be done at any position , But when writing content , It will only be appended at the end of the file .

Close file fclose(FILE*)

Read and write a single character

1、 read fgetc(FILE*)
Read unsigned char return int type , If the file ends or an error is encountered, return EOF,fgetc() And getc() The two functions are consistent , The difference is that fgetc() It's a function ,getc() Is the implementation of macros , Macro is a little faster , But macros may call parameters repeatedly , Parameters with side effects such as fp++ It may become fp++++++
2、 Write fputc(int c,FILE*)
c Is the character to be written , Successful return of written characters , If there is an error, return EOF,fputc() And putc() The difference is the same as 1

Read and write the whole string

1、fgets(char * s,int n,FILE*)
s Is the storage address for reading characters ,int Is the number of reads n-1, Leave a plus \0, If there is an error, it will not overwrite s The content of the string pointed to
2、fputs(char *s,FILE*)
The parameters are the same as above

Format read-write file

1、 write in ：fprint(FILE*,“%d%f…”,int ,float…)
2、 Read ：fscanf(FILE*, Read in format , Data storage location )

FILE* fp;
int a;
fscanf(fp,"%d",&a);// A number of the read file is stored in a in 

Binary read-write ：
fread() And fwrite() They all have four parameters ,ptr Is the data storage address pointer , The second is to read the memory block size , The third is to read the number , The last one is the file pointer

FILE *fp;
struct book *tm=(struct book*)malloc(sizeof(struct book));
// Initialization omitted 
fwrite(tm,sizeof(struct book),1,fp);// hold tm The data in is written in fp in 
struct book *um=(struct book*)malloc(sizeof(struct book));
fread(um,sizeof(struct book),1,fp);// hold fp The data read in is stored in um in 

Random, speaking, reading and writing

ftell(FILE*), The return value is usually long int type , It is understood that the file is a large array , Return to cursor position
rewind(FILE*), Call this function to move the cursor to the beginning of the file
Move cursor function fseek(FILE*,long int,whence)：

FILE*fp;
fseek(fp,4,SEEK_SET);// Move the cursor to four bytes after the beginning of the file 
fseek(fp,4,SEEK_CUR);// Move the cursor to four bytes behind the current position 
fseek(fp,-4,SEEK_END);// Move the cursor to the first four bytes at the end of the file 

Be careful ： Before each of the above operations on the file, you must first open the file and then close it （ I omitted ）, Prevent data reading and writing errors