I am trying to use the CString.replace method and seem to not be replacing the rest of the string.
tmpStr.Replace(_T('in.'), _T(' '));
is the specific line. I want to remove all instances of the string "in." in the CString tmpStr. But it seems it only to replace the 'i' in "in." with a space. And the rest it leave alone.
Is there a way to replace a string with a string?
You're not calling the overload that you intend to call. CString::Replace has an overload that takes two characters, that's the one your function call invokes. Change 'in.' to "in." (note the double quotes instead of single quotes). Similarly, change ' ' to " ".
'in.' is a multicharacter literal, and how this is interpreted is implementation defined. It seems VC just considers it to be the same as i.
Related
I'm really confused about the escape character " \ " and its relation to the windows file system. In the following example:
char* fwdslash = "c:/myfolder/myfile.txt";
char* backslash = "c:\myfolder\myfile.txt";
char* dblbackslash = "c:\\myfolder\\myfile.txt";
std::ifstream file(fwdslash); // Works
std::ifstream file(dblbackslash); // Works
std::ifstream file(backslash); // Doesn't work
I get what you are doing here is escaping a special character so you can use it in this string. In no way by placing a backslash in a string literal or std::string do you actually change the string ---
---Edit: This is completely wrong, and the source of my confusion---
So it seems that the escape character is only treated by certain classes or things to mean something other than a backslash, like outputting on the console, ie., std::cout << "\hello"; will not print the backslash. In the case of ifstream (or I'm not sure if the same applies with the C fopen() version), it must be that this class or function treats backslashes as escape characters. I'm wondering, since the Windows file system uses backslashes wouldn't it make sense for it to accept the simple string with backslashes, ie., "c:\myfolder\myfile.txt" ? Trying it this way fails.
Also, in my compiler (Visual Studio) when I include headers I can use .\ and ..\ to mean either the current folder, or the parent folder. I'm pretty sure the \ in this isn't related to the escape character, but are these forms specific to Windows, part of the C preprocessor, or part of the C or C++ language? I know that backslashes are a Windows thing, so I can't see any reason another system would expect backslashes even when using .\ and ..\
Thanks.
In no way by placing a backslash in a string literal[...] do you
actually change the string
You do. Compiler actually modifies literal you wrote before embedding it into compiled program. If a backslash is found in string or character literal while parsing source code it is ignored and next character is treated specially. \n becomes carriage return, etc. For escaped characters without special meaning threatment is implementation defined. Usually it just means character unchanged.
You cannot just pass "c:\myfolder\file.txt" because it is not a string which will be seen by your program. Your program will see "c:myfolderfile.txt" instead. This is why escaped backslash has a special meaning, to allow embedding backslashes in actual string your program will see.
The solution is to either escape your backslashes, or use raw string literals (C++11 onwards):
const char* path = R"(c:\myfolder\file.txt)"
Filenames given to #include directive are not string literals, even if they are in form "path\to\header", so substitution rules are not applied to them.
The single backwards slash practically escapes the next character. In order to get rid of this behavior you need to double escape it. Now for the forward slash, it is probably a compatibility issue which follows the Unix tradition.
Similar thing to this is also in the Java world. A single forward slash is treated for path separation on both Windows and Unix, while also a double backslash.
To make it more clear why single backslash doesn't work, just remember that the following String practically produces a newline, a backslash and a tab:
"\n\\\t"
i.e. in an example like:
""c:\my\next\file.txt"
would actually produce:
"c:my
ext
ile.txt"
(the double space is form feed, see here)
Because when declaring a cstring literal the backslashes escape the next character, for special characters. This is so you can do newlines (\n), nulls (\0), carriage returns (\r) etc...
char* backslash = "c:\myfolder \myfile.txt";
I'm currently facing an issue with a method parsing a string to another method. The problem is that I want to prevent it from using possible escape sequences.
The string I want to parse is not constant so (as far as I know) using the R declaration to make it a raw literal is not applicable here since I have to use variables.
Furthermore, in some cases there is user input included into the string (unconverted), so simply escaping those sequences by replacing a "\" character with "\\" is not an option either, the input can include those sequences too.
To be more precise on the issue:
A string formatted like f.e. " "\x10\x4 \x6(" " is getting auto compiled and converted into a non-human readable format as soon as it gets parsed to the next function. I want to prevent that conversion without In order to get the exact same string in the next function which needs to work with it.
Hope someone can help me since I'm new to c++ programming. Thanks in advance :D
#include "pch.h"
#include <iostream>
int main()
{
stringTester stringtester;
std::string test = stringtester.exampleString();
stringtester.stringOutput(test);
}
std::string stringTester::exampleString()
{
std::string exampleInput = "\x10\x5\x1a\aTestInput\\n \x6(";
return exampleInput;
}
void stringTester::stringOutput(std::string test)
{
std::cout << test << std::endl;
}
The actual output her (copied from console) is " TestInput\n ( ", whereas the wanted output would be the original string "\x10\x5\x1a\aTestInput\n \x6("
Edit: It seems like on SO it can't show the unknown characters. There are xtra characters in front and after the "TestInput\n ("
When you write a string literal in your source code the compiler replaces escape sequences with the character that they represent. That's why the quoted string in your example gets turned into nonsense. The way to fix that is to either replace each backslash with two backslashes or to make it a raw string literal.
When your program reads text input it doesn't do any of those adjustments. So if the code does
std::string input;
std::cin >> input;
and the user types the characters \x10\x5\x1a\aTestInput\\n \x6( into the console, input will end up with the characters \x10\x5\x1a\aTestInput\\n \x6(.
Once you've got the string, whether as a string literal or as text from the console, you can do whatever you want with it.
You have two possibilities for a backslash to remain a backslash in your C/C++ strings (and Java, JavaScript, PHP...)
Double all the Backslashes
Just as you said, you want to double all backslashes. This is fine. If the input was:
\\\\
Then your C/C++ string is going to be:
"\\\\\\\\"
(a mouthful, I know...)
Use the Hex/Octal Character
The other way, if you don't like the double backslash too much (if it scares you, somehow), is to use the character sequence in octal or hex (or Unicode in newer versions):
\ becomes "\134" or "\x5C"
As you may notice, though, this means 4 characters per backslash. So most people will generally just double the backslash (one 2 characters). Plus the double backslash is well understood. The code point may not be as well known by programmers coming behind you.
As a side note, if your user can enter any character, then they can also enter the double quote (") character. It is important that you also escape those. You can similarly use the backslash and the double quote character or its code point:
\" or \042 or \x22
I'm just starting out on Fortran and am confused with the usage of double vs single quotation marks.
They are equivalent. There is no difference in their usage.
You can employ this to print one of the quotation characters:
print *, "'"
print *, '"'
prints first ' and then ".
Note: You can also use two quote characters in a row to print one:
print *, """"
print *, ''''
prints first " and then '.
Functionally they have no difference. Just try to be consistent about which one you use. If your strings tend to have double quotes in them, use single quotes everywhere; if you use single quotes more often, use double quotes to delimit your strings.
As an additional note, it is possible to escape the quote character inside a string: (i.e. 'You\'re') but most people would suggest using it doubled up as they would find it more readable (i.e. 'You''re').
there are some differences.
write (6,*) " Bruce's beard "
is fine and successfully print out Bruce's beard.
However,
write (6,*) '' Bruce's beard ''
write (6,*) ' Bruce's beard '
will not give you correct output which should be Bruce's beard.
Outside comments and character contexts, the special characters " (quotation mark/quote) and ' (apostrophe) are used in two ways:
delimiting a literal character constant, including one used as a character string edit descriptor
delimiting a BOZ literal constant
The syntax rules for both of these explicitly allow either " or ' to be used as a delimiter (but require the start and end delimiters to match, so they aren't quite interchangeable as characters), with no difference in interpretation between the two cases. (This contrasts with some other languages where only one form may be allowed, or each form may mean something different.)
In Fortran 2018, R724 allows both "A" and 'A' as literal character constants; R766 allows both O'1' and O"1" in specifying an octal constant. (Naturally, "A' and O"1' are not allowed by these rules.)
Within literal character constants/character contexts, as shown in other answers here, each special character represents its own particular form. Again, note from the other answers how, for example, '"A''A"' is to be interpreted.
Within a comment, neither character has any particular interpretation.
I'm really confused about the escape character " \ " and its relation to the windows file system. In the following example:
char* fwdslash = "c:/myfolder/myfile.txt";
char* backslash = "c:\myfolder\myfile.txt";
char* dblbackslash = "c:\\myfolder\\myfile.txt";
std::ifstream file(fwdslash); // Works
std::ifstream file(dblbackslash); // Works
std::ifstream file(backslash); // Doesn't work
I get what you are doing here is escaping a special character so you can use it in this string. In no way by placing a backslash in a string literal or std::string do you actually change the string ---
---Edit: This is completely wrong, and the source of my confusion---
So it seems that the escape character is only treated by certain classes or things to mean something other than a backslash, like outputting on the console, ie., std::cout << "\hello"; will not print the backslash. In the case of ifstream (or I'm not sure if the same applies with the C fopen() version), it must be that this class or function treats backslashes as escape characters. I'm wondering, since the Windows file system uses backslashes wouldn't it make sense for it to accept the simple string with backslashes, ie., "c:\myfolder\myfile.txt" ? Trying it this way fails.
Also, in my compiler (Visual Studio) when I include headers I can use .\ and ..\ to mean either the current folder, or the parent folder. I'm pretty sure the \ in this isn't related to the escape character, but are these forms specific to Windows, part of the C preprocessor, or part of the C or C++ language? I know that backslashes are a Windows thing, so I can't see any reason another system would expect backslashes even when using .\ and ..\
Thanks.
In no way by placing a backslash in a string literal[...] do you
actually change the string
You do. Compiler actually modifies literal you wrote before embedding it into compiled program. If a backslash is found in string or character literal while parsing source code it is ignored and next character is treated specially. \n becomes carriage return, etc. For escaped characters without special meaning threatment is implementation defined. Usually it just means character unchanged.
You cannot just pass "c:\myfolder\file.txt" because it is not a string which will be seen by your program. Your program will see "c:myfolderfile.txt" instead. This is why escaped backslash has a special meaning, to allow embedding backslashes in actual string your program will see.
The solution is to either escape your backslashes, or use raw string literals (C++11 onwards):
const char* path = R"(c:\myfolder\file.txt)"
Filenames given to #include directive are not string literals, even if they are in form "path\to\header", so substitution rules are not applied to them.
The single backwards slash practically escapes the next character. In order to get rid of this behavior you need to double escape it. Now for the forward slash, it is probably a compatibility issue which follows the Unix tradition.
Similar thing to this is also in the Java world. A single forward slash is treated for path separation on both Windows and Unix, while also a double backslash.
To make it more clear why single backslash doesn't work, just remember that the following String practically produces a newline, a backslash and a tab:
"\n\\\t"
i.e. in an example like:
""c:\my\next\file.txt"
would actually produce:
"c:my
ext
ile.txt"
(the double space is form feed, see here)
Because when declaring a cstring literal the backslashes escape the next character, for special characters. This is so you can do newlines (\n), nulls (\0), carriage returns (\r) etc...
char* backslash = "c:\myfolder \myfile.txt";
According to the manual, string concatenation isn't implemented in gdb. I need it however, so is there a way to achieve this, perhaps using array functions?
I don't have a copy of gdb around to try this on, but perhaps this line from later in the Ada section of the document will help you?
Rather than use catenation and
symbolic character names to introduce
special characters into strings, one
may instead use a special bracket
notation, which is also used to print
strings. A sequence of characters of
the form ["XX"]' within a string or
character literal denotes the (single)
character whose numeric encoding is XX
in hexadecimal. The sequence of
characters["""]' also denotes a
single quotation mark in strings. For
example, "One line.["0a"]Next
line.["0a"]"
contains an ASCII newline character
(Ada.Characters.Latin_1.LF) after each
period.
For Objective-C:
[#"asd" stringByAppendingString:#"zxc"]
[#"ID: " stringByAppendingString:(NSString*) [aTaskDict valueForKey:#"ID"]]