{"id":20068,"date":"2022-11-08T15:46:58","date_gmt":"2022-11-08T10:16:58","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-how-do-i-check-if-a-string-format-is-valid-while-reading-from-a-text-file-in-c-closed\/"},"modified":"2022-11-08T15:46:58","modified_gmt":"2022-11-08T10:16:58","slug":"solved-how-do-i-check-if-a-string-format-is-valid-while-reading-from-a-text-file-in-c-closed","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-how-do-i-check-if-a-string-format-is-valid-while-reading-from-a-text-file-in-c-closed\/","title":{"rendered":"[Solved] How do i check if a string format is valid while reading from a text file in C++? [closed]"},"content":{"rendered":"

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When I give out my answer, it’s yet unclear that what name your input text file has. Let’s suppose the name of your text file is test.txt<\/code> and it locates right within the same directory as the C++ source file, test.cpp<\/code>.<\/p>\n

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test.txt<\/p>\n<\/blockquote>\n

Car,Red,ZX342DC\n<\/code><\/pre>\n
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test.cpp<\/p>\n<\/blockquote>\n
#include <fstream>\n#include <string>\n#include <regex>\n#include <iostream>\n\nusing namespace std;\n\nint main()\n{\n    \/\/ Let's start with variable declaration and initialization\n\n    \/\/ First you have to open the text file,\n    \/\/ for which you need `ifstream`.\n    \/\/ It is responsible for decoding text files.\n    ifstream ifs(\"test.txt\");\n\n    \/\/ Provide a temporary storage for each line\n    string line;\n\n    \/\/ Regular expression pattern object\n    \/\/ This is what you need\n    \/\/ in order to validate each line\n    \/\/ and extract data from each line,\n    regex p(\"(\\\\w+),(\\\\w+),([A-Z]{2}[0-9]{3}[A-Z]{2})\");\n\n    \/\/ Match object\n    smatch m;\n\n    \/\/ Check if the file stream is opened\n    \/\/ otherwise you might have some problems\n    \/\/ to continue the following steps\n    if (ifs.is_open())\n    {\n        \/\/ Then you need to traverse over each line in the file.\n        for (int lineNum = 1;\n                getline(ifs, line);\n                lineNum++)\n        {\n            \/\/ Validate the line\n            if (regex_search(line, m, p) && m.size() > 3)\n            {\n                cout << \"Pattern matched.\" << endl;\n                cout << endl;\n\n                string vehicle = m.str(1);\n                string color = m.str(2);\n                string plate = m.str(3);\n\n                cout << \"Vehicle:\\t\"    << vehicle << endl;\n                cout << \"Color  :\\t\"    << color << endl;\n                cout << \"Plate  :\\t\"    << plate << endl;\n\n                \/\/ You can insert some codes here to handle the results\n\n                cout << endl;\n            }\n            else\n            {\n                cerr << \"There's an invalid entry in line number - \" << lineNum << \"!\" << endl;\n            }\n        }\n\n        \/\/ Always remember to close a stream\n        \/\/ before exiting the program\n        \/\/ otherwise you may suffer from **memory leakage**\n        ifs.close();\n    }\n    else\n    {\n        cerr << \"Fail to open input file!\" << endl;\n    }\n\n    return 0;\n}\n<\/code><\/pre>\n
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Reference:<\/p>\n