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Efficient Input/Output Stream Manipulation in C: Redirection and Reading Text from a File

Are you new to C programming and looking for ways to manipulate input/output streams efficiently? We have got you covered! In this article, we will discuss two fundamental concepts- “

Using File Redirection in C” and “

Reading Input Text from a File.” These concepts are essential to help you efficiently read input text from a file and understand how you can redefine standard input in C to make your program more flexible.

Using File Redirection in C

File redirection is one of the most useful techniques for manipulating input/output streams in the C programming language. When you redirect a file, you tell the operating system to change the source or the destination of the input/output stream of the program.

Here’s how:

Redefining Standard Input:

In C programming, the input stream (stdin) is represented by a pre-defined FILE pointer called “stdin.” You can use the < operator to tell the application to use a file instead of the standard input stream. The fgets() function is used to read characters from the file stream and store them in a buffer.

Suppose we want to read from a file called “input.txt” using the standard input method. Here’s how you do it:

“`

fgets(buffer, MAX_SIZE, stdin);

“`

The fgets function reads the input from stdin stream and stores it in the buffer with a maximum size of MAX_SIZE.

The < operator is used to redirect the input from the file input.txt:

“`

./myprogram < input.txt

“`

Here, myprogram is the executable file that you want to run, and input.txt is the name of the file from which you want to read the input.

Allocating Dynamic Memory

When the size of the input file is not predetermined, you need to allocate memory dynamically using the malloc() function. To determine the size of the file, you can use the “stat” system call and read the file’s size in bytes.

Here’s an example of how you can allocate memory dynamically to read input from the file:

“`

int main(int argc, char** argv) {

// Checking if the command-line argument is supplied

if (argc != 2) {

printf(“nInvalid argumentsn”);

exit(1);

}

// Opening the file

FILE* file = fopen(argv[1], “r”);

if (file == NULL) {

printf(“nFailed to open file: %sn”, argv[1]);

exit(1);

}

//Finding the file size

struct stat fileStat;

if (stat(argv[1], &fileStat) < 0) {

printf(“nFailed to read file sizen”);

exit(1);

}

long fileSize = fileStat.st_size;

// Allocating memory

char* buffer = malloc(fileSize * sizeof(char));

if (buffer == NULL) {

printf(“nFailed to allocate memoryn”);

exit(1);

}

// Reading the file

fread(buffer, 1, fileSize, file);

printf(“%s”, buffer);

// Closing the file

fclose(file);

return 0;

}

“`

Here, the program checks if the appropriate number of command-line arguments was provided. If the arguments are incorrect, the program exits with an error message.

Once the file is opened, it finds the file size using the stat function. Next, it allocates memory using the malloc() function.

After allocating memory, the program reads the file’s contents using the fread() function, prints it on the console using printf() function, close the file, and deallocates memory using free() function.

Reading Input Text from a File

In this section, we will discuss how to read input text from a file efficiently.

Retrieving File Size

Before reading the input text from a file, the first thing you need to do is determine the size of the file. To retrieve the file size in C, you can use the stat() system call.

The function takes the file’s pathname as an argument and fills the struct stat’s structure, which contains the file’s size in bytes.

Here’s an example code snippet that retrieves the file size:

“`

int main(int argc, char *argv[]) {

struct stat st;

char *filename = argv[1];

if (stat(filename, &st) == 0) {

printf(“File Size: %lu bytesn”, st.st_size);

}

else {

printf(“Failed to get file size.n”);

}

return 0;

}

“`

Here, the program passes the file’s path as an argument to the stat system call, which retrieves the size of the file.

The size is stored in the “st” structure, which is then printed on the console.

Storing Input Text

Once you know the file size, you can allocate memory dynamically using the malloc() function and read the file. The fgets() function is used to read input text from the file line by line and store it in a buffer of fixed size.

Here’s a code example that shows how to read the input text from a file:

“`

int main(int argc, char *argv[]) {

FILE *fp;

char *filename = argv[1];

char buffer[255];

fp = fopen(filename, “r”);

if (fp == NULL) {

printf(“Failed to open file.n”);

exit(1);

}

while (fgets(buffer, 255, fp)) {

printf(“%s”, buffer);

}

fclose(fp);

return 0;

}

“`

Here, the program opens the file in read mode using the fopen() function and checks if the file exists. If the file does not exist, the program exits with an error message.

After successfully opening the file, the program reads the file line by line using the fgets() function and stores it in a buffer of size 255. Finally, the program prints the buffer on the console using the printf() function.

Conclusion

In conclusion, using file redirection and reading input text from a file is essential to manipulate input/output streams in the C programming language efficiently. Understanding how to redefine standard input, allocate dynamic memory, and read input text efficiently is essential for creating sophisticated applications.

We hope this article has provided a helpful introduction to these essential concepts. In this article, we’ve discussed two fundamental concepts regarding manipulating input/output streams efficiently in C programming.

We explored how to redefine the standard input by using file redirection, and how to allocate dynamic memory and read input text from a file. These techniques are fundamental to creating sophisticated applications and streamlining your code’s functionality.

By understanding these concepts, developers can improve application development by making it more efficient and flexible. Overall, mastering these techniques is fundamental to ensure successful completion of C programming projects.

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