C language Review of Android JNI: file read/write and random number Functions

C language is more suitable for operating hardware and is more efficient in some file processing operations, so similar operations generally use JNI to call C code for operations: such as audio, video and image processing:

For example, in audio format Transcoder, similar to photo's rendering of image effects and other applications, a large number of JNI applications are required.

Here we will review the content of the C language operation file:

C file operation mode:

"RT" only opens a text file and only supports reading data.
"WT" only writes to open or create a text file, only data can be written
Append "at" to open a text file and write data at the end of the file.
"Rb" is used to open a binary file and only read data.
"WB" only writes to open or create a binary file, only data can be written
Append "AB" to open a binary file and write data at the end of the file.
"RT +" reads and writes to open a text file, allowing reading and writing
"WT +" reads and writes to open or create a text file, allowing reading and writing
"At +" to open a text file, allow reading, or append data at the end of the file
"RB +" reads and writes a binary file, allowing reading and writing
"WB +" to open or create a binary file and allow reading and writing
"AB +" reads and writes to open a binary file, allowing reading or appending data at the end of the file

The usage of files is described as follows:

The usage of a file is composed of R, W, A, T, B, and +. The meanings of each character are as follows:

R (read): Read
W (write): Write
A (append): append
T (text): Text File, can be omitted without writing
B (banary): Binary File

Write a file in C language:

// Java file = new file ();-> C open a file
// Fos = fileoutputstrem (File)-> C. Get the output stream int Len = FOS. Write () of the file. // how long the data is written?

// FOS. Write ();-C Write File. Fos. Flush ();

# Include <stdio. h>
Main (){
// File * fopen (char * filename, char * type );
// Sharedpreference world_readable world_writeable append private

File * fp = fopen ("1.txt"," WT ");
// Int fwrite (void * PTR, int size, int nitems, file * stream );

// The returned value int indicates the number of successful writes.

// Void * The data to be written to the file by PTR can be char * int *
// Size the length of data written at a time.
// Nitems indicates the number of writes.
// Stream is written to that file.
Char * STR = "hello ";
Int result = fwrite (STR, sizeof (char), 5, FP );
Printf ("% d write times \ n", result );
// It must be called. If it is not called, the file will be occupied.
Fclose (FP );

System ("pause ");
}

C language:
# Include <stdio. h>
Main (){
// File * fopen (char * filename, char * type );
// Sharedpreference world_readable world_writeable append private

File * fp = fopen ("1.txt"," RT ");
// Int fread (void * PTR, int size, int nitems, file * stream );
// The returned value int indicates the number of times the size is actually read.
// * Memory space in which PTR data is read
// Size the length of data read at a time is multiple bytes
// How many times does nitmes read data?
// The file from which stream is read
Char * STR = (char *) malloc (sizeof (char) * 10); // allocate memory
Int READ = fread (STR, sizeof (char), 5, FP );

Printf ("% d times read \ n", read );


Printf ("str = % s \ n", STR );
Free (STR); // manually release the allocated memory
Fclose (FP); // close the stream
System ("pause ");
}

# Include <stdlib. h>
# Include <stdio. h>

Random Number function in C language:

To use the rand () function, you need to import the stdlib. h and stdio. h header files.

# Include <stdlib. h>
# Include <stdio. h>

Int getpressure (){
// The underlying C implementation code. The internal working principle may be very complicated and we don't care about it.

// Method name parameters and return values
Return rand () % 300; // 0 ~ 300

}