Let’s look at the common file operations in C:<\/strong><\/p>\n1. Creating a New File<\/h4>\n
The fopen() function can be used to create a new file.<\/p>\n
FILE *fp;\r\nfp = fopen(\"data.txt\",\"w\"); \/\/create data.txt file in write mode<\/pre>\nThe first parameter is the filename, and the second parameter is the mode “w” for write.<\/p>\n
2. Opening an Existing File<\/h4>\n
To open an existing file, specify the filename and appropriate mode while calling fopen():<\/strong><\/p>\nFILE *fp;\r\n\r\n\/\/open text.txt in read mode\r\nfp = fopen(\"text.txt\",\"r\");\r\n\r\n\/\/open image.jpeg in binary write mode \r\nfp = fopen(\"image.jpeg\",\"wb\");<\/pre>\n3. Closing a File<\/h4>\n
Always close opened files using fclose(fp) when done. This frees up resources and prevents data corruption:<\/strong><\/p>\nfclose(fp); \/\/close file pointed by fp<\/pre>\n4. Writing to a File<\/h4>\n
1. Writing to a Text File<\/strong><\/p>\nTo write to a text file, we can use functions like fprintf(), fputc(), etc.<\/p>\n
Example:<\/strong><\/p>\n#include <stdio.h>\r\n\r\nint main() {\r\n\r\n FILE *fpointer = fopen(\"data.txt\",\"w\");\r\n \r\n fprintf(fpointer, \"This is some text\\n\");\r\n fprintf(fpointer, \"Written to a file\\n\");\r\n \r\n fclose(fpointer);\r\n \r\n return 0;\r\n}<\/pre>\nThis writes the given text to data.txt.<\/p>\n
We can also write individual characters using fputc():<\/strong><\/p>\nfputc('A', fpointer); \/\/writes character 'A' to file<\/pre>\nAlways check the return value from writing functions to catch errors:<\/strong><\/p>\nif(fprintf(fpointer, text) < 0) {\r\n \/\/error occurred\r\n printf(\"Unable to write to file\");\r\n}<\/pre>\n2. Writing to a Binary File<\/strong><\/p>\nFor binary files, we use the fwrite() function.<\/p>\n
Example:<\/strong><\/p>\n#include <stdio.h>\r\n\r\nstruct Record {\r\n char name[30];\r\n int age;\r\n float salary;\r\n};\r\n\r\nint main() {\r\n\r\n struct Record r1 = {\"John\", 30, 4000};\r\n \r\n FILE *fp = fopen(\"data.bin\",\"wb\");\r\n \r\n fwrite(&r1, sizeof(struct Record), 1, fp);\r\n \r\n fclose(fp);\r\n\r\n return 0;\r\n}<\/pre>\nThis writes the struct to the binary file data.bin.<\/p>\n
We can write multiple structs like this in a loop.<\/p>\n
5. Reading from a File<\/h4>\n
1. Reading from a Text File<\/strong><\/p>\nTo read from a text file, use fscanf(), fgetc() and related functions.<\/p>\n
Example:<\/strong><\/p>\n#include <stdio.h>\r\n\r\nint main() {\r\n\r\n char str[100];\r\n int num;\r\n \r\n FILE *fptr = fopen(\"text.txt\",\"r\");\r\n \r\n if(fptr == NULL) {\r\n printf(\"Error opening file\"); \r\n return 1;\r\n }\r\n \r\n \/\/read string from file\r\n fscanf(fptr,\"%s\", str); \r\n \r\n \/\/read integer\r\n fscanf(fptr, \"%d\", &num); \r\n\r\n printf(\"String is: %s\\n\", str);\r\n printf(\"Integer is: %d\", num);\r\n \r\n fclose(fptr);\r\n\r\n return 0;\r\n}<\/pre>\nThis reads a string and integer from the text file text.txt.<\/p>\n
We can also read individual characters using fgetc(fptr).<\/p>\n
Always check for end of file (EOF) condition to avoid errors while reading:<\/strong><\/p>\nwhile(!feof(fptr)) {\r\n \/\/keep reading from file\r\n}<\/pre>\n2. Reading from a Binary File<\/strong><\/p>\n#include <stdio.h>\r\n\r\nstruct Record {\r\n char name[30];\r\n int age;\r\n float salary;\r\n};\r\n\r\nint main() {\r\n\r\n struct Record r;\r\n \r\n FILE *fp = fopen(\"data.bin\",\"rb\");\r\n \r\n if(fp == NULL) {\r\n printf(\"Error opening file\");\r\n return 1;\r\n }\r\n\r\n \/\/read struct from file\r\n fread(&r, sizeof(struct Record), 1, fp);\r\n\r\n printf(\"Name: %s\\n\", r.name); \r\n printf(\"Age: %d\\n\", r.age);\r\n printf(\"Salary: %f\", r.salary);\r\n\r\n fclose(fp);\r\n \r\n return 0;\r\n}<\/pre>\nThis reads the struct from binary file data.bin into r.<\/p>\n
Opening Modes in Standard I\/O<\/h3>\n
\n\n\n| Opening Mode<\/b><\/td>\n | Description<\/b><\/td>\n | If File Does Not Exist<\/b><\/td>\n<\/tr>\n\n| r<\/span><\/td>\n | Open for reading only.<\/span><\/td>\n | Returns NULL.<\/span><\/td>\n<\/tr>\n\n| rb<\/span><\/td>\n | Open for reading only in binary mode.<\/span><\/td>\n | Returns NULL.<\/span><\/td>\n<\/tr>\n\n| w<\/span><\/td>\n | Open for writing only. Overwrites existing content.<\/span><\/td>\n | Creates new file.<\/span><\/td>\n<\/tr>\n\n| wb<\/span><\/td>\n | Open for writing only in binary mode. Overwrites existing content.<\/span><\/td>\n | Creates new file.<\/span><\/td>\n<\/tr>\n\n| a<\/span><\/td>\n | Open for appending only. Data is added to the end of file.<\/span><\/td>\n | Creates new file.<\/span><\/td>\n<\/tr>\n\n| ab<\/span><\/td>\n | Open for appending only in binary mode. Data added to end of file.<\/span><\/td>\n | Creates new file.<\/span><\/td>\n<\/tr>\n\n| r+<\/span><\/td>\n | Open for both reading and writing.<\/span><\/td>\n | Returns NULL.<\/span><\/td>\n<\/tr>\n\n| rb+<\/span><\/td>\n | Open for both reading and writing in binary mode.<\/span><\/td>\n | Returns NULL.<\/span><\/td>\n<\/tr>\n\n| w+<\/span><\/td>\n | Open for reading and writing. Overwrites existing content.<\/span><\/td>\n | Creates new file.<\/span><\/td>\n<\/tr>\n\n| wb+<\/span><\/td>\n | Open for reading and writing in binary mode. Overwrites existing content.<\/span><\/td>\n | Creates new file.<\/span><\/td>\n<\/tr>\n\n| a+<\/span><\/td>\n | Open for reading and appending.<\/span><\/td>\n | Creates new file.<\/span><\/td>\n<\/tr>\n\n| ab+<\/span><\/td>\n | Open for reading and appending in binary mode.<\/span><\/td>\n | Creates new file.<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nHandling Errors and Exceptions in C<\/h3>\nSome common file operation errors:<\/strong><\/p>\n\n- File open failure<\/li>\n
- File read\/write failure<\/li>\n
- Trying to read at EOF<\/li>\n
- File not found<\/li>\n
- Access violations<\/li>\n<\/ul>\n
Ways to handle errors:<\/strong><\/p>\n\n- Check return values from file functions like fopen(), fread() etc.<\/li>\n
- Use perror() to print the error message for the last error that occurred.<\/li>\n
- Check for EOF using feof() while reading.<\/li>\n
- Use descriptive error messages and clean up resources properly.<\/li>\n<\/ul>\n
Advanced File Operations<\/h3>\n1. Using fseek() for Positioning<\/h4>\nThe fseek() function allows moving the file position indicator to a desired location:<\/strong><\/p>\nfseek(fptr, offset, fromwhere);<\/pre>\nThe offset is number of bytes. fromwhere can be:<\/strong><\/p>\n\n- SEEK_SET – start of file<\/li>\n
- SEEK_CUR – current position<\/li>\n
- SEEK_END – end of file<\/li>\n<\/ul>\n
Example:<\/strong><\/p>\n#include <stdio.h>\r\n\r\nstruct Record {\r\n int id;\r\n \/\/other fields\r\n};\r\n\r\nint main() {\r\n\r\n struct Record r;\r\n\r\n FILE *fp = fopen(\"records.bin\",\"rb\");\r\n \r\n \/\/move pointer to end\r\n fseek(fp, 0, SEEK_END); \r\n \r\n \/\/read last record\r\n fseek(fp, -sizeof(struct Record), SEEK_CUR);\r\n fread(&r, sizeof(struct Record), 1, fp);\r\n\r\n \/\/print last record's id\r\n printf(\"Last ID: %d\", r.id);\r\n \r\n fclose(fp);\r\n\r\n return 0;\r\n}<\/pre>\nThis reads the last record in reverse order from a binary file.<\/p>\n Best Practices and Tips<\/h3>\nSome tips for efficient file handling:<\/strong><\/p>\n\n- Always check if the file opening was successful before further operations.<\/li>\n
- Use relative paths instead of absolute file paths for portability.<\/li>\n
- Close all opened files using fclose() before program termination.<\/li>\n
- Use binary mode for non-textual data for performance.<\/li>\n
- Handle errors and exceptions properly for robustness.<\/li>\n
- Use fseek() and ftell() for random file access.<\/li>\n<\/ul>\n
Conclusion<\/h3>\nFile handling allows storing persistent data for later use, leading to efficient and robust C programs. The key concepts include opening, closing, reading and writing files in different modes. By following best practices and error handling, we can build powerful applications using file handling in C.<\/p>\n","protected":false},"excerpt":{"rendered":" File Handling in C File handling is an essential concept in C programming. It allows preserving data even after the program execution is over. This makes it simple to efficiently store and access vast...<\/p>\n","protected":false},"author":86671,"featured_media":123905,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[19488],"tags":[29967,23914,29133,2263,29966,23948,29965],"class_list":["post-123309","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-c-programming","tag-c-file-handling","tag-c-programming","tag-c-tutorials","tag-c","tag-file-handling","tag-file-handling-in-c","tag-how-to-read-and-write-data-from-file-in-c"],"yoast_head":"\n How to Write and Read Data from File in C - DataFlair<\/title>\n<meta name=\"description\" content=\"The key concepts of file handling in C include opening, closing, reading and writing files in different modes.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"How to Write and Read Data from File in C - DataFlair\" \/>\n<meta property=\"og:description\" content=\"The key concepts of file handling in C include opening, closing, reading and writing files in different modes.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/\" \/>\n<meta property=\"og:site_name\" content=\"DataFlair\" \/>\n<meta property=\"article:publisher\" content=\"https:\/\/www.facebook.com\/DataFlairWS\/\" \/>\n<meta property=\"article:published_time\" content=\"2024-02-19T12:30:56+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2024-02-19T12:47:25+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2023\/11\/how-to-write-and-read-data-from-file-in-c.webp\" \/>\n\t<meta property=\"og:image:width\" content=\"1200\" \/>\n\t<meta property=\"og:image:height\" content=\"628\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/webp\" \/>\n<meta name=\"author\" content=\"TechVidvan Team\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:creator\" content=\"@DataFlairWS\" \/>\n<meta name=\"twitter:site\" content=\"@DataFlairWS\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"TechVidvan Team\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"5 minutes\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"How to Write and Read Data from File in C - DataFlair","description":"The key concepts of file handling in C include opening, closing, reading and writing files in different modes.","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/","og_locale":"en_US","og_type":"article","og_title":"How to Write and Read Data from File in C - DataFlair","og_description":"The key concepts of file handling in C include opening, closing, reading and writing files in different modes.","og_url":"https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/","og_site_name":"DataFlair","article_publisher":"https:\/\/www.facebook.com\/DataFlairWS\/","article_published_time":"2024-02-19T12:30:56+00:00","article_modified_time":"2024-02-19T12:47:25+00:00","og_image":[{"width":1200,"height":628,"url":"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2023\/11\/how-to-write-and-read-data-from-file-in-c.webp","type":"image\/webp"}],"author":"TechVidvan Team","twitter_card":"summary_large_image","twitter_creator":"@DataFlairWS","twitter_site":"@DataFlairWS","twitter_misc":{"Written by":"TechVidvan Team","Est. reading time":"5 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/#article","isPartOf":{"@id":"https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/"},"author":{"name":"TechVidvan Team","@id":"https:\/\/data-flair.training\/blogs\/#\/schema\/person\/0e594f928e31fc96628ac40f6ae74f49"},"headline":"How to Write and Read Data from File in C","datePublished":"2024-02-19T12:30:56+00:00","dateModified":"2024-02-19T12:47:25+00:00","mainEntityOfPage":{"@id":"https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/"},"wordCount":905,"commentCount":0,"publisher":{"@id":"https:\/\/data-flair.training\/blogs\/#organization"},"image":{"@id":"https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/#primaryimage"},"thumbnailUrl":"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2023\/11\/how-to-write-and-read-data-from-file-in-c.webp","keywords":["c file handling","c programming","c tutorials","C++","file handling","File Handling in C","how to read and write data from file in c"],"articleSection":["C Tutorials"],"inLanguage":"en-US","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/#respond"]}]},{"@type":"WebPage","@id":"https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/","url":"https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/","name":"How to Write and Read Data from File in C - DataFlair","isPartOf":{"@id":"https:\/\/data-flair.training\/blogs\/#website"},"primaryImageOfPage":{"@id":"https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/#primaryimage"},"image":{"@id":"https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/#primaryimage"},"thumbnailUrl":"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2023\/11\/how-to-write-and-read-data-from-file-in-c.webp","datePublished":"2024-02-19T12:30:56+00:00","dateModified":"2024-02-19T12:47:25+00:00","description":"The key concepts of file handling in C include opening, closing, reading and writing files in different modes.","breadcrumb":{"@id":"https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/#breadcrumb"},"inLanguage":"en-US","potentialAction":[{"@type":"ReadAction","target":["https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/"]}]},{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/#primaryimage","url":"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2023\/11\/how-to-write-and-read-data-from-file-in-c.webp","contentUrl":"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2023\/11\/how-to-write-and-read-data-from-file-in-c.webp","width":1200,"height":628,"caption":"how to write and read data from file in c"},{"@type":"BreadcrumbList","@id":"https:\/\/data-flair.training\/blogs\/how-to-write-read-data-from-file-in-c\/#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Blog Home","item":"https:\/\/data-flair.training\/blogs\/"},{"@type":"ListItem","position":2,"name":"C Tutorials","item":"https:\/\/data-flair.training\/blogs\/category\/c-programming\/"},{"@type":"ListItem","position":3,"name":"How to Write and Read Data from File in C"}]},{"@type":"WebSite","@id":"https:\/\/data-flair.training\/blogs\/#website","url":"https:\/\/data-flair.training\/blogs\/","name":"DataFlair","description":"Learn Today. Lead Tomorrow.","publisher":{"@id":"https:\/\/data-flair.training\/blogs\/#organization"},"potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/data-flair.training\/blogs\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-US"},{"@type":"Organization","@id":"https:\/\/data-flair.training\/blogs\/#organization","name":"DataFlair","url":"https:\/\/data-flair.training\/blogs\/","logo":{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/data-flair.training\/blogs\/#\/schema\/logo\/image\/","url":"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2016\/07\/Data-Flair.png","contentUrl":"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2016\/07\/Data-Flair.png","width":106,"height":48,"caption":"DataFlair"},"image":{"@id":"https:\/\/data-flair.training\/blogs\/#\/schema\/logo\/image\/"},"sameAs":["https:\/\/www.facebook.com\/DataFlairWS\/","https:\/\/x.com\/DataFlairWS","https:\/\/www.linkedin.com\/company\/dataflair-web-services-pvt-ltd\/","https:\/\/www.youtube.com\/user\/DataFlairWS"]},{"@type":"Person","@id":"https:\/\/data-flair.training\/blogs\/#\/schema\/person\/0e594f928e31fc96628ac40f6ae74f49","name":"TechVidvan Team","image":{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/secure.gravatar.com\/avatar\/c89190da3d4010c71ba476b618ab10fdc2335c82cdfa0ad5002d98d0f2473444?s=96&d=mm&r=g","url":"https:\/\/secure.gravatar.com\/avatar\/c89190da3d4010c71ba476b618ab10fdc2335c82cdfa0ad5002d98d0f2473444?s=96&d=mm&r=g","contentUrl":"https:\/\/secure.gravatar.com\/avatar\/c89190da3d4010c71ba476b618ab10fdc2335c82cdfa0ad5002d98d0f2473444?s=96&d=mm&r=g","caption":"TechVidvan Team"},"description":"TechVidvan Team provides high-quality content & courses on AI, ML, Data Science, Data Engineering, Data Analytics, programming, Python, DSA, Android, Flutter, full stack web dev, MERN, and many latest technology.","url":"https:\/\/data-flair.training\/blogs\/author\/test001\/"}]}},"amp_enabled":true,"_links":{"self":[{"href":"https:\/\/data-flair.training\/blogs\/wp-json\/wp\/v2\/posts\/123309","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/data-flair.training\/blogs\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/data-flair.training\/blogs\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/data-flair.training\/blogs\/wp-json\/wp\/v2\/users\/86671"}],"replies":[{"embeddable":true,"href":"https:\/\/data-flair.training\/blogs\/wp-json\/wp\/v2\/comments?post=123309"}],"version-history":[{"count":4,"href":"https:\/\/data-flair.training\/blogs\/wp-json\/wp\/v2\/posts\/123309\/revisions"}],"predecessor-version":[{"id":131836,"href":"https:\/\/data-flair.training\/blogs\/wp-json\/wp\/v2\/posts\/123309\/revisions\/131836"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/data-flair.training\/blogs\/wp-json\/wp\/v2\/media\/123905"}],"wp:attachment":[{"href":"https:\/\/data-flair.training\/blogs\/wp-json\/wp\/v2\/media?parent=123309"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/data-flair.training\/blogs\/wp-json\/wp\/v2\/categories?post=123309"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/data-flair.training\/blogs\/wp-json\/wp\/v2\/tags?post=123309"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}} | | | | | | | | | | | | |