文件读写

read and write file

Last updated on May. 9, 2024, created on May. 6, 2024.

数据文件分为两类：文本文件（ASCII）、二进制文件（Binary）

文件变量的类型为：FILE，利用它可以创建文件指针变量：FILE *f;

文件打开函数：f=fopen("C:\\mytext.txt","r");

打开文件的常见方式：

Method	Type	Permission	Existence	Return Value	Annotation
r	File	Read Only	Necessary	Successful: File* (head of the file) Failed: NULL
r+	File	Read and Write	Necessary	Successful: File* (head of the file) Failed: NULL
rb+	Binary	Read and Write	Necessary	Successful: File* (head of the file) Failed: NULL
rt+	ASCII	Read and Write	Necessary	Successful: File* (head of the file) Failed: NULL
w	File	Write Only	Not Necessary	Successful: File* (head of the file) Failed: NULL	(1) If the file to be open already exists, the contents will be overwritten; if not, computer will create a new file. (2) If the file to be open is not editable, the function will return NULL.
w+	File	Read and Write	Not Necessary	Successful: File* (head of the file) Failed: NULL	(1) If the file to be open already exists, the contents will be overwritten; if not, computer will create a new file. (2) If the file to be open is not editable, the function will return NULL.
a	File	Write Only(Add Only)	Not Necessary	Successful: File* (head of the file) Failed: NULL	(1) If the file to be open already exists, the contents will be overwritten; if not, computer will create a new file. (2) If the file to be open is not editable, the function will return NULL.
a+	File	Read and Write(Add Only)	Not Necessary	Successful: File* (head of the file) Failed: NULL	(1) If the file to be open already exists, the contents will be overwritten; if not, computer will create a new file. (2) If the file to be open is not editable, the function will return NULL. (3) Read from the head of the file and add from the end.

文件关闭函数：fclose(f);

注意：

文件关闭成功则返回0，反之程序返回EOF（-1）

文件读写的常见方式：

Method	Description	Return Value
ch1=fgetc(f);	Read a character	Successful: one character Failed: EOF(-1)
fputc('a',f);	Write a character	Successful: the character you write Failed: EOF(-1)
fgets(ch,n,f);	Read a string with a length of n-1, the last character is '\0', and store it in ch. Note that '\n' will also be read if it is before the end of reading process.	Successful: address of ch Failed: NULL
fputs(ch,f);	Write a string	Successful: 0 Failed: non-zero value
fscanf(f,format,ch);	Formatted read a string	Successful: count Failed: EOF(-1)
fprintf(f,format,ch);	Formatted write a string	Successful: count Failed: EOF(-1)
fread(ch,size,count,f);	Read a data block	Successful: (actual/successful-read-data)count Failed: 0
fwrite(ch,size,count,f);	Write a data block	Successful: (actual/successful-read-data)count Failed: 0

文件指针的常见用法：

Method	Annotation
fseek(f,(long int)offset,origin);	offset:10L(10 bytes after origin),-30L(30 bytes before origin) origin:0(begin),1(current),2(end)
ftell(f);	This method can be adopted to calculate the size of file.
rewind(f);	Move the pointer to the beginning of the file.
feof(f);	Judge if pointer points to the end of the file.
rename(old_filename,new_filename);	Rename a file.
remove(filename);	Remove a file.