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C > Small Programs Code Examples

WAV file player

/* WAV file player WARNING: You need a HUGE memory model to run this. */ #include "ALLOC.H" #include "DOS.H" #include "CONIO.H" #include "STDIO.H" void main() { char *name; printf(" Enter the file name...:"); scanf("%s",name); playwav(name,1.0); } void playwav(char wavefile[14],float delaytime); struct WaveData { unsigned int SoundLength, Frequency; char *Sample; }; struct HeaderType { long RIFF; //RIFF header char NI1 [18]; //not important unsigned int Channels; //channels 1 = mono; 2 = stereo long Frequency; //sample frequency char NI2 [6]; //not important char BitRes; //bit resolution 8/16 bit char NI3 [12]; //not important } Header; struct WaveData Voice; //Pointer to wave file unsigned int Base; //Sound Blaster base address char WaveFile [25]; //File name for the wave file to be played / Checks to see if a Sound Blaster exists at a given address, returns true if Sound Blaster found, false if not. / int ResetDSP(unsigned int Test) { //Reset the DSP outportb (Test + 0x6, 1); delay(10); outportb (Test + 0x6, 0); delay(10); //Check if (reset was succesfull if ((inportb(Test + 0xE) & 0x80 == 0x80) && (inportb(Test + 0xA) == 0xAA)) { //DSP was found Base = Test; return (1); } else //No DSP was found return (0); } / Send a byte to the DSP (Digital Signal Processor) on the Sound Blaster / void WriteDSP(unsigned char Value) { //Wait for the DSP to be ready to accept data while ((inportb(Base + 0xC) & 0x80) == 0x80); //Send byte outportb (Base + 0xC, Value); } / Plays a part of the memory/ void PlayBack (struct WaveData *Wave) { long LinearAddress; unsigned int Page, OffSet; unsigned char TimeConstant; TimeConstant = (65536 - (256000000 / Wave->Frequency)) >> 8; WriteDSP(0x40); //DSP-command 40h - Set sample frequency WriteDSP(TimeConstant); //Write time constant //Convert pointer to linear address LinearAddress = FP_SEG (Wave->Sample); LinearAddress = (LinearAddress << 4) + FP_OFF (Wave->Sample); Page = LinearAddress >> 16; //Calculate page OffSet = LinearAddress & 0xFFFF; //Calculate offset in the page /* Note - this procedure only works with DMA channel 1 */ outportb (0x0A, 5); //Mask DMA channel 1 outportb (0x0C, 0); //Clear byte pointer outportb (0x0B, 0x49); //Set mode /* The mode consists of the following: 0x49 = binary 01 00 10 01 | | | | | | | +- DMA channel 01 | | +---- Read operation (the DSP reads from memory) | +------- Single cycle mode +---------- Block mode */ outportb (0x02, OffSet & 0x100); //Write the offset to the DMA controller outportb (0x02, OffSet >> 8); outportb (0x83, Page); //Write the page to the DMA controller outportb (0x03, Wave->SoundLength & 0x100); outportb (0x03, Wave->SoundLength >> 8); outportb (0x0A, 1); //Unmask DMA channel WriteDSP(0x14); // DSP-command 14h - Single cycle playback WriteDSP(Wave->SoundLength & 0xFF); WriteDSP(Wave->SoundLength >> 8); } / Loads a wave file into memory. This procedure expects a _very_ standard wave header. It doesn't perform much error checking. / int LoadVoice (struct WaveData *Voice, char *FileName) { FILE *WAVFile; //If it can't be opened... WAVFile = fopen(FileName, "rb"); if (WAVFile == NULL) { //..display error message return (0); } //Return length of file for sound length minus 48 bytes for .WAV header fseek(WAVFile, 0L, SEEK_END); Voice->SoundLength = ftell (WAVFile) - 48; fseek(WAVFile, 0L, SEEK_SET); //Check RIFF header if (Voice->SoundLength > 32000) { if (Voice->SoundLength > 64000) { Voice->SoundLength = 64000; } } free(Voice->Sample); Voice->Sample = (char *)malloc(Voice->SoundLength); //Assign memory if (!Voice->Sample) { return (0); } //Load the sample data fread(&Header, 46, 1, WAVFile); //Check RIFF header if (Header.RIFF != 0x46464952) { printf ("Not a wave file "); return (0); } //Check channels if (Header.Channels != 1) { printf ("Not a mono wave file "); return (0); } //Check bit resolution if (Header.BitRes != 8) { printf ("Not an 8-bit wave file "); return (0); } Voice->Frequency = Header.Frequency; //Load the sample data fread(Voice->Sample, Voice->SoundLength + 2, 1, WAVFile); fclose (WAVFile); //Close the file return (1); } void playwav (char wavefile[14], float delaytime ) { delaytime=1.0; if (ResetDSP (0x220)) { //at 220h printf (""); } else { if (ResetDSP (0x240)) { //at 240h printf (""); } else { //or none at all printf (""); return; } } //Load wave file if (LoadVoice (&Voice, wavefile)) { //Start playback PlayBack (&Voice); delay(delaytime*1000); //Stops DMA-transfer WriteDSP (0xD0); } }

Allocate memory block. Allocates a block of size bytes of memory, returning a pointer to the beginning of the block. The content of the newly allocated block of memory is not initialized, remaining with indeterminate values. If size is zero, the return value depends on the particular library implementation (it may or may not be a null pointer), but the returned pointer shall not be dereferenced. The "malloc" or "memory allocation" method in C is used to dynamically allocate a single large block of memory with the specified size. It returns a pointer of type void which can be cast into a pointer of any form. It doesn't Iniatialize memory at execution time so that it has initializes each block with the default garbage value initially.

The bitwise operators are the operators used to perform the operations on the data at the bit-level. When we perform the bitwise operations, then it is also known as bit-level programming. It consists of two digits, either 0 or 1. It is mainly used in numerical computations to make the calculations faster. We have different types of bitwise operators in the C programming language. The following is the list of the bitwise operators: Bitwise AND operator is denoted by the single ampersand sign (&). Two integer operands are written on both sides of the (&) operator. If the corresponding bits of both the operands are 1, then the output of the bitwise AND operation is 1; otherwise, the output would be 0.

Get current position in stream. Returns the current value of the position indicator of the stream. For binary streams, this is the number of bytes from the beginning of the file. For text streams, the numerical value may not be meaningful but can still be used to restore the position to the same position later using fseek (if there are characters put back using ungetc still pending of being read, the behavior is undefined). On success, the current value of the position indicator is returned. On failure, -1L is returned, and errno is set to a system-specific positive value.

Pointers in C are easy and fun to learn. Some C programming tasks are performed more easily with pointers, and other tasks, such as dynamic memory allocation, cannot be performed without using pointers. So it becomes necessary to learn pointers to become a perfect C programmer. Let's start learning them in simple and easy steps. As you know, every variable is a memory location and every memory location has its address defined which can be accessed using ampersand (&) operator, which denotes an address in memory. Consider the following example, which prints the address of the variables defined. A pointer is a variable whose value is the address of another variable, i.e., direct address of the memory location. Like any variable or constant, you must declare a pointer before using it to store any variable address. The general form of a pointer variable declaration is:

While loop is also known as a pre-tested loop. In general, a while loop allows a part of the code to be executed multiple times depending upon a given boolean condition. It can be viewed as a repeating if statement. The while loop is mostly used in the case where the number of iterations is not known in advance. The while loop evaluates the test expression inside the parentheses (). If test expression is true, statements inside the body of while loop are executed. Then, test expression is evaluated again. The process goes on until test expression is evaluated to false. If test expression is false, the loop terminates.

In C, the "main" function is treated the same as every function, it has a return type (and in some cases accepts inputs via parameters). The only difference is that the main function is "called" by the operating system when the user runs the program. Thus the main function is always the first code executed when a program starts. main() function is a user defined, body of the function is defined by the programmer or we can say main() is programmer/user implemented function, whose prototype is predefined in the compiler. Hence we can say that main() in c programming is user defined as well as predefined because it's prototype is predefined. main() is a system (compiler) declared function whose defined by the user, which is invoked automatically by the operating system when program is being executed.

An expression containing logical operator returns either 0 or 1 depending upon whether expression results true or false. Logical operators are commonly used in decision making in C programming. These operators are used to perform logical operations and used with conditional statements like C if-else statements.

Closes a file descriptor, fildes. This frees the file descriptor to be returned by future open() calls and other calls that create file descriptors. The fildes argument must represent a hierarchical file system (HFS) file. When the last open file descriptor for a file is closed, the file itself is closed. If the file's link count is 0 at that time, its space is freed and the file becomes inaccessible. When the last open file descriptor for a pipe or FIFO file is closed, any data remaining in the pipe or FIFO file is discarded. close() unlocks (removes) all outstanding record locks that a process has on the associated file. Behavior for sockets: close() call shuts down the socket associated with the socket descriptor socket, and frees resources allocated to the socket. If socket refers to an open TCP connection, the connection is closed. If a stream socket is closed when there is input data queued, the TCP connection is reset rather than being cleanly closed.

The open() function shall establish the connection between a file and a file descriptor. It shall create an open file description that refers to a file and a file descriptor that refers to that open file description. The file descriptor is used by other I/O functions to refer to that file. The path argument points to a pathname naming the file. The open() function shall return a file descriptor for the named file that is the lowest file descriptor not currently open for that process. The open file description is new, and therefore the file descriptor shall not share it with any other process in the system. The FD_CLOEXEC file descriptor flag associated with the new file descriptor shall be cleared.

The if...else statement executes two different codes depending upon whether the test expression is true or false. Sometimes, a choice has to be made from more than 2 possibilities. The if...else ladder allows you to check between multiple test expressions and execute different statements. In C/C++ if-else-if ladder helps user decide from among multiple options. The C/C++ if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the C else-if ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.

Open file. Opens the file whose name is specified in the parameter filename and associates it with a stream that can be identified in future operations by the FILE pointer returned. The operations that are allowed on the stream and how these are performed are defined by the mode parameter. The returned stream is fully buffered by default if it is known to not refer to an interactive device (see setbuf). The returned pointer can be disassociated from the file by calling fclose or freopen. All opened files are automatically closed on normal program termination.

Read formatted data from stdin. Reads data from stdin and stores them according to the parameter format into the locations pointed by the additional arguments. The additional arguments should point to already allocated objects of the type specified by their corresponding format specifier within the format string. In C programming, scanf() is one of the commonly used function to take input from the user. The scanf() function reads formatted input from the standard input such as keyboards. The scanf() function enables the programmer to accept formatted inputs to the application or production code. Moreover, by using this function, the users can provide dynamic input values to the application.

Close file. Closes the file associated with the stream and disassociates it. All internal buffers associated with the stream are disassociated from it and flushed: the content of any unwritten output buffer is written and the content of any unread input buffer is discarded. Even if the call fails, the stream passed as parameter will no longer be associated with the file nor its buffers.

#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program. Here are the two types of file that can be included using #include:

The free() function in C library allows you to release or deallocate the memory blocks which are previously allocated by calloc(), malloc() or realloc() functions. It frees up the memory blocks and returns the memory to heap. It helps freeing the memory in your program which will be available for later use. In C, the memory for variables is automatically deallocated at compile time. For dynamic memory allocation in C, you have to deallocate the memory explicitly. If not done, you may encounter out of memory error.

Writes the C string pointed by format to the standard output (stdout). If format includes format specifiers (subsequences beginning with %), the additional arguments following format are formatted and inserted in the resulting string replacing their respective specifiers. printf format string refers to a control parameter used by a class of functions in the input/output libraries of C programming language. The string is written in a simple template language: characters are usually copied literally into the function's output, but format specifiers, which start with a % character, indicate the location and method to translate a piece of data (such as a number) to characters. "printf" is the name of one of the main C output functions, and stands for "print formatted". printf format strings are complementary to scanf format strings, which provide formatted input (parsing). In both cases these provide simple functionality and fixed format compared to more sophisticated and flexible template engines or parsers,

Read block of data from stream. Reads an array of count elements, each one with a size of size bytes, from the stream and stores them in the block of memory specified by ptr. The position indicator of the stream is advanced by the total amount of bytes read. The total amount of bytes read if successful is (size*count).

Delay function is used to suspend execution of a program for a particular time. delay() function requires a parameter which should be a number, defining the milliseconds for the delay. To use delay function in your program you should include the "dos.h" header file which is not a part of standard C library. Here unsigned int is the number of milliseconds (remember 1 second = 1000 milliseconds).

Reposition stream position indicator. Sets the position indicator associated with the stream to a new position. For streams open in binary mode, the new position is defined by adding offset to a reference position specified by origin. For streams open in text mode, offset shall either be zero or a value returned by a previous call to ftell, and origin shall necessarily be SEEK_SET. If the function is called with other values for these arguments, support depends on the particular system and library implementation (non-portable). The end-of-file internal indicator of the stream is cleared after a successful call to this function, and all effects from previous calls to ungetc on this stream are dropped.