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Dec 16th, 2007

reading a text file and searching for a sentence

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Hello,

i need help on how to search for a sentence inside a txt file after opening it and then applying a condition if that sentence was found.

im a beginner so i don't know how.

basically i have written a program that uses system("command>file.txt") to start a command line process and write the output to a file , and what i want is to search for a certain line in the output (an error message for example) and force the program to act upon the condition of it being found.

c++ Syntax (Toggle Plain Text)
string sentencetolookup="error connecting to server";
system("command>output.txt");
string sentencetolookup="error connecting to server";
system("command>output.txt");

i want to know how to look for "sentencetolookup" inside the "output.txt" file and if found force the program to stop or return an error message.

any help is appreciated
thanks

hashinclude

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Dec 16th, 2007

Re: reading a text file and searching for a sentence

you need an ifstream object to open the text file, and a string to receive the strings. Both of these are standard c++ classes in <fstream> and <string> header files. There are hundreds, if not thousands, of examples you can follow to write your program so I am not going to repeat them here. Basically you need to (1) read a line using getline function then (2) compare it to the string you are looing for using the == comparison operator.

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Re: reading a text file and searching for a sentence

Click to Expand / Collapse Quote originally posted by Ancient Dragon ...

you need an ifstream object to open the text file, and a string to receive the strings. Both of these are standard c++ classes in <fstream> and <string> header files. There are hundreds, if not thousands, of examples you can follow to write your program so I am not going to repeat them here. Basically you need to (1) read a line using getline function then (2) compare it to the string you are looing for using the == comparison operator.

thanks, i did view alot of pages talking about ifstream, the best thing i could come up with is read a whole text file , i couldn't find anything on how to read specific lines or read all lines one by one and compare each to a string, all examples showed the use of an array as a buffer to read a txt file instead of a string when i compared an array to a string nothing happened

the whole reason im resorting to txt files is because i couldn't figure out how to obtain any returned results (error or successful completion) by other programs , i am using an exe that renames a computer (netdom) and i have a c++ program that would call that exe using the system() function but i want my program to terminate or loop back to the beginning if the exe file returned an error (like computer account already exists or anything of that sort)

hashinclude

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Dec 16th, 2007

Re: reading a text file and searching for a sentence

You didn't look hard enough. Didn't you run across the getline() method?

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Dec 17th, 2007

Re: reading a text file and searching for a sentence

i did look hard enough to find and use the getline() method , and i was able to read the whole txt file, but i didn't know where to go or what to do after that, how to lookup a sentence by searching each line in the txt file and then if it is found, tell my program do this and that

Last edited by hashinclude; Dec 17th, 2007 at 1:28 am.

hashinclude

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Re: reading a text file and searching for a sentence

Maybe this will help. Note the title...

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Dec 17th, 2007

Re: reading a text file and searching for a sentence

in that case can anyone point me to where there is a very detailed tutorial on how to use ifstream ?

hashinclude

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Dec 17th, 2007

Re: reading a text file and searching for a sentence

Click to Expand / Collapse Quote originally posted by hashinclude ...

in that case can anyone point me to where there is a very detailed tutorial on how to use ifstream ?

I guess I was too subtle. Post your code as the link describes. Very often if we see the code we can figure out what to tell you. So far we're only guessing.

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Re: reading a text file and searching for a sentence

c++ Syntax (Toggle Plain Text)
int main()
{
 
		char str[5000];
		char errorline[]="grab this text";
		system("command>output.txt");
                fstream file_op("output.txt",ios::in);
		 while(!file_op.eof())
                 {
                         file_op.getline(str,5000);
                         cout <<str;
                 }  
		 if(str==errorline)
		 {
			 cout<<"\nerror found\n";
			 return 0;
		 }
 
		 file_op.close();
                 system("pause");
		 return 0;
 
 
}
int main()
{
	
		char str[5000];
		char errorline[]="grab this text";
		system("command>output.txt");
                fstream file_op("output.txt",ios::in);
		 while(!file_op.eof())
                 {
                         file_op.getline(str,5000);
                         cout <<str;
                 }  
		 if(str==errorline)
		 {
			 cout<<"\nerror found\n";
			 return 0;
		 }

		 file_op.close();
                 system("pause");
		 return 0;


}

you can see that i can only know how to open the file and read it into str array but i don't know how to search the whole file or a certain line or all lines for a string of text that matches errorline

hashinclude

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Re: reading a text file and searching for a sentence

line 6: do you have a program on your computer called command.exe ? If not then that line of code will do nothing other than get an error message from the operating system that "command not found".

lines 8 and 10: that loop doesn't work right. You need to combine them like this:

C++ Syntax (Toggle Plain Text)
while( file_op.getline(str,5000) )
{
    // compare the strings here to see if this line is the one you are looking for
}
while( file_op.getline(str,5000) )
{
    // compare the strings here to see if this line is the one you are looking for
}

line 13: you can not compare two c-style character arrays like that. Use strcpy() to do that
if( strcpy(errorline, str) == 0)

Last edited by Ancient Dragon; Dec 17th, 2007 at 9:03 am.

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