**Course Title:** Mastering C: From Fundamentals to Advanced Programming **Section Title:** File I/O in C **Topic:** File operations: fopen, fclose, fread, fwrite, fprintf, fscanf ### Introduction to File Operations In the previous topic, we discussed the different types of files in C, including text and binary files. In this topic, we will delve into the various file operations that can be performed in C, including opening, closing, reading, writing, and scanning files. ### Opening a File: fopen() The `fopen()` function is used to open a file in C. It returns a file pointer of type `FILE *` that is used to perform various operations on the file. The syntax for `fopen()` is as follows: ```c FILE *fopen(const char *filename, const char *mode); ``` The `filename` parameter specifies the name of the file to be opened, and the `mode` parameter specifies the mode in which the file is to be opened. The different modes are listed below: * `r`: Opens the file in read mode. The file must exist. * `w`: Opens the file in write mode. If the file does not exist, it will be created. If the file already exists, its contents will be deleted. * `a`: Opens the file in append mode. If the file does not exist, it will be created. If the file already exists, data will be appended to the end of the file. * `r+`: Opens the file in read and write mode. The file must exist. * `w+`: Opens the file in read and write mode. If the file does not exist, it will be created. If the file already exists, its contents will be deleted. * `a+`: Opens the file in read and append mode. If the file does not exist, it will be created. If the file already exists, data will be appended to the end of the file. Example: ```c #include <stdio.h> int main() { FILE *filePtr; filePtr = fopen("example.txt", "w"); if (filePtr == NULL) { printf("Could not open file\n"); return 1; } printf("File opened successfully\n"); fclose(filePtr); return 0; } ``` ### Closing a File: fclose() The `fclose()` function is used to close a file in C. It returns an integer value indicating whether the operation was successful. The syntax for `fclose()` is as follows: ```c int fclose(FILE *stream); ``` Example: ```c #include <stdio.h> int main() { FILE *filePtr; filePtr = fopen("example.txt", "w"); if (filePtr == NULL) { printf("Could not open file\n"); return 1; } printf("File opened successfully\n"); if (fclose(filePtr) != 0) { printf("Could not close file\n"); return 1; } printf("File closed successfully\n"); return 0; } ``` ### Reading from a File: fread() The `fread()` function is used to read data from a file in C. It returns the number of items successfully read. The syntax for `fread()` is as follows: ```c size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream); ``` The `ptr` parameter specifies the pointer to the array where the data is to be stored. The `size` parameter specifies the size of each item, and the `nmemb` parameter specifies the number of items to be read. The `stream` parameter specifies the file pointer. Example: ```c #include <stdio.h> int main() { FILE *filePtr; int num; filePtr = fopen("example.txt", "r"); if (filePtr == NULL) { printf("Could not open file\n"); return 1; } if (fread(&num, sizeof(int), 1, filePtr) != 1) { printf("Could not read from file\n"); return 1; } printf("Number read: %d\n", num); fclose(filePtr); return 0; } ``` ### Writing to a File: fwrite() The `fwrite()` function is used to write data to a file in C. It returns the number of items successfully written. The syntax for `fwrite()` is as follows: ```c size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream); ``` The `ptr` parameter specifies the pointer to the array where the data is stored. The `size` parameter specifies the size of each item, and the `nmemb` parameter specifies the number of items to be written. The `stream` parameter specifies the file pointer. Example: ```c #include <stdio.h> int main() { FILE *filePtr; int num = 10; filePtr = fopen("example.txt", "w"); if (filePtr == NULL) { printf("Could not open file\n"); return 1; } if (fwrite(&num, sizeof(int), 1, filePtr) != 1) { printf("Could not write to file\n"); return 1; } printf("Number written successfully\n"); fclose(filePtr); return 0; } ``` ### Formatted Input/Output: fprintf() and fscanf() The `fprintf()` and `fscanf()` functions are used to perform formatted input/output operations in C. The syntax for `fprintf()` is as follows: ```c int fprintf(FILE *stream, const char *format, ...); ``` The syntax for `fscanf()` is as follows: ```c int fscanf(FILE *stream, const char *format, ...); ``` Example: ```c #include <stdio.h> int main() { FILE *filePtr; int num; filePtr = fopen("example.txt", "w"); if (filePtr == NULL) { printf("Could not open file\n"); return 1; } fprintf(filePtr, "%d", 10); fclose(filePtr); filePtr = fopen("example.txt", "r"); if (filePtr == NULL) { printf("Could not open file\n"); return 1; } fscanf(filePtr, "%d", &num); printf("Number read: %d\n", num); fclose(filePtr); return 0; } ``` ### Key Takeaways * Use `fopen()` to open a file in C, and specify the mode in which the file is to be opened. * Use `fclose()` to close a file in C, and check the return value to ensure the operation was successful. * Use `fread()` to read data from a file in C, and specify the size of each item and the number of items to be read. * Use `fwrite()` to write data to a file in C, and specify the size of each item and the number of items to be written. * Use `fprintf()` and `fscanf()` to perform formatted input/output operations in C, and specify the format of the data to be read or written. ### Practice Exercise Try to create a program that reads a file containing a list of numbers, calculates the sum of the numbers, and writes the result to another file. Use the `fopen()`, `fclose()`, `fread()`, `fwrite()`, `fprintf()`, and `fscanf()` functions to perform the necessary file operations. ### Further Reading For more information on file operations in C, refer to the following resources: * [The C Standard Library](https://en.cppreference.com/w/c) - File I/O * [C Programming Language Tutorial](https://www.w3schools.com/c/c_file_handling.asp) - File Handling in C * [GNU C Library](https://www.gnu.org/software/libc/documentation.html) - File Input and Output ### Leave a Comment/Ask for Help If you have any questions or need help with the material covered in this topic, leave a comment below.