{"id":12797,"date":"2022-10-01T23:14:35","date_gmt":"2022-10-01T17:44:35","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-segmentation-fault-from-sscanf-in-a-loop-in-c\/"},"modified":"2022-10-01T23:14:35","modified_gmt":"2022-10-01T17:44:35","slug":"solved-segmentation-fault-from-sscanf-in-a-loop-in-c","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-segmentation-fault-from-sscanf-in-a-loop-in-c\/","title":{"rendered":"[Solved] Segmentation fault from sscanf in a loop in C"},"content":{"rendered":"

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Using feof()<\/code> is a bad idea as it can return zero, and then the next line of input can encounter end of the file – which can give unexpected errors<\/p>\n

Also fgets()<\/code> returns NULL<\/code> if an error occurs, including encountering end of file.<\/p>\n

Imagine your loop has been going along happily, and has just read the second last line in the file. On the next iteration, feof()<\/code> will return zero, so the first statement strings = fgets(strings, __MAXLEN__, prova)<\/code> will succeed. The second one – inside the do-while<\/code> loop – will set strings<\/code> to NULL<\/code>, so will pass the NULL<\/code> to your readCompl()<\/code> function – which will, in turn, try to read from the NULL<\/code> using sscanf()<\/code>. sscanf()<\/code> gives undefined behaviour if given a NULL<\/code> – (one symptom of which can be a segmentation violation – the program accessing memory it shouldn’t).<\/p>\n

The solution needs to be in two parts. Firstly, don’t use feof()<\/code> to control any loop. Second, check the result of functions you call (fgets()<\/code>, sscanf()<\/code>, etc) and – if you need to – use their return value to control loops.<\/p>\n<\/p><\/div>\n

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1<\/span> <\/p><\/div>\n<\/div>\n

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solved Segmentation fault from sscanf in a loop in C <\/p>\n","protected":false},"excerpt":{"rendered":"

[ad_1] Using feof() is a bad idea as it can return zero, and then the next line of input can encounter end of the file – which can give unexpected errors Also fgets() returns NULL if an error occurs, including encountering end of file. Imagine your loop has been going along happily, and has just … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[324,493,585,1187,362],"class_list":["post-12797","post","type-post","status-publish","format-standard","hentry","category-solved","tag-c","tag-file","tag-scanf","tag-segmentation-fault","tag-string"],"yoast_head":"\n[Solved] Segmentation fault from sscanf in a loop in C - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-segmentation-fault-from-sscanf-in-a-loop-in-c\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] Segmentation fault from sscanf in a loop in C - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] Using feof() is a bad idea as it can return zero, and then the next line of input can encounter end of the file – which can give unexpected errors Also fgets() returns NULL if an error occurs, including encountering end of file. Imagine your loop has been going along happily, and has just ... 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