Suppose s is
a
b
c
const std::string s =
std::cout << R"( s )" << std::endl;
How to std::cout the content of the string in raw literal? I mean the cout return the value in this format: "a\nb\nc".
I need to transform a very large text into a std::string.
I cant use fileread as i need to define its value inside the src.
What you would need to do is to scan the string, and replace all occurrences of the characters you are interested in (such as carriage return, tab, etc) with printable escape sequence and than print this new text.
Here is somewhat crude proof of concept:
std::string escape(std::string_view src) {
std::string ret;
ret.reserve(src.size() * 2); // at worst, the string consists solely of escapable symbols
static constexpr std::array escapable = {std::make_pair('\t', 't'),
std::make_pair('\n', 'n')}; // add more chars as needed, note that the array is sorted
for (const char ch: src) {
std::pair search_pair{ch, ' '};
auto esc_char = std::equal_range(escapable.begin(), escapable.end(), search_pair, [](auto& a, auto& b) { return a.first < b.first; });
if (esc_char.first != escapable.end()) {
ret.push_back('\\');
ret.push_back(esc_char.first->second);
} else {
ret.push_back(ch);
}
}
return ret;
}
Now, you can use it:
const std::string str = "A\nbub\tfuf\n";
std::cout << escape(str) << "\n";
Above snippet prints A\nbub\tfuf\n
You could be interested by the JSON specification.
You could consider serializing your data in JSON format using open source C++ libraries like jsoncpp
You could also consider using some YAML format with the yaml-cpp library
You could be interested by the SWIG tool which generates C++ glue code.
You could consider using binary data formats like XDR.
You should specify (on paper, with a pencil) your data format in EBNF notation and use ANTLR or GNU bison to generate the parser (the printer is easier to code)
The RefPerSys project (an open source symbolic artificial intelligence system, GPLv3+ licensed) is persisting data in textual format. You may borrow some code are re-use it in your application, if you obey to that GPL license.
Look also into Qt or POCO frameworks, but notice that DWORD64 is not a standard C++ type. See this C++ reference and read a recent C++ standard (like n3337 or better).
Consider generating your C++ serializing code
With tools like GNU m4 or GPP (or your own one).
Pitrat's book Artificial Beings: the Conscience of a Conscious Machine (ISBN-13: 978-1848211018) should give you valuable insight and intuitions.
You can load this text file into a std::string like this:
Store the text in your file, e.g. mystring.txt, as a raw string literal in the format R"(raw_characters)":
R"(Run.M128A XmmRegisters[16];
BYTE Reserved4[96];", Run.CONTEXT64 := " DWORD64 P1Home;
DWORD64 P2Home;
...
)"
#include the file into a string:
namespace
{
const std::string mystring =
#include "mystring.txt"
;
}
Your IDE might flag this up as a syntax error, but it isn't. What you're doing is loading the contents of file directly into the string at compile time.
Finally print the string:
std::cout << mystring << std::endl;
Why not just save the escaped version of the string in the file?
Any way, here's a function to 'escape' characters:
#include <iostream>
#include <string>
#include <unordered_map>
std::string replace_all(const std::string &mystring)
{
const std::unordered_map<char, std::string> lookup =
{ {'\n', "\\n"}, {'\t', "\\t"}, {'"', "\\\""} };
std::string new_string;
new_string.reserve(mystring.length() * 2);
for (auto c : mystring)
{
auto it = lookup.find(c);
if (it != lookup.end())
new_string += it->second;
else
new_string += c;
}
return new_string;
}
int main() {
std::string mystring = R"(Run.M128A XmmRegisters[16];
BYTE Reserved4[96];", Run.CONTEXT64 := " DWORD64 P1Home;
DWORD64 P2Home;
DWORD64 P3Home;
DWORD64 P4Home;
DWORD64 P5Home;
DWORD64 P6Home;)";
auto new_string = replace_all(mystring);
std::cout << new_string << std::endl;
return 0;
}
Here's a demo.
I have a vector of strings which was created from parsing a config file. All the strings should be in the format key=value. I'd like to iterate over the vector, and use the putenv function to set an environment variable to the key-value pair.
The code:
for(auto it = settings.begin(); it != settings.end(); it++) {
try {
auto i = it - settings.begin();
cout << i << endl;
putenv(settings.at(i));
} catch (...) {
cout << "Config is not in the format key=value ... please correct" << endl;
}
}
This throws the error:
cannot convert ‘__gnu_cxx::__alloc_traits<std::allocator<std::basic_string<char> > >::value_type {aka std::basic_string<char>}’ to ‘char*’ for argument ‘1’ to ‘int putenv(char*)’
I'm very new to C++, and all these variable types and pointers are confusing me.
You're mixing C and C++ stuff.
Your vector contains C++ strings, std::string.
putenv is an "old" function expecting a pointer to a char buffer, i.e. a C-string.
Fortunately, std::string makes it easy to get one of those:
putenv(settings.at(i).c_str());
// ^^^^^^^^
However, there is still a problem there. putenv takes "ownership" of the buffer you give it, and expects it to last "forever". Yours won't; it'll only be there until the std::string is modified or destroyed. Not good enough!
Conventionally, we use C's strdup here to allocate a copy of the char buffer. It's then putenv's (or the OS's) responsibility to free it later.
putenv(strdup(settings.at(i).c_str()));
// ^^^^^^^ ^
Since putenv is not in the C or C++ standard, but is provided by POSIX, you should check the manpages for your operating system to make sure you're using it correctly.
The error is caused by your call to putenv(), which expects a pointer to char's. Your vector contains C++ strings (std::string)...
You can try this:
for (auto setting : settings) {
// ... putenv() is inconsistent across compilers, so use setenv() instead...
std::string key = item.substr( 0, item.find_first_of( "=" ) ) ;
std::string val = item.substr( key.length()+1 ) ;
if ( setenv( key.c_str(), val.c_str(), 1 ) != 0 ) {
cerr << "setenv(" << key << ',' << val << ") has failed: " << strerror( errno ) << endl;
}
}
From what I've read, putenv should be avoided in new code, and setenv should be used, as it makes a copy of its arguments, regardless of compiler version.
(setenv is in stdlib.h)
Is there a way to include an entire text file as a string in a C program at compile-time?
something like:
file.txt:
This is
a little
text file
main.c:
#include <stdio.h>
int main(void) {
#blackmagicinclude("file.txt", content)
/*
equiv: char[] content = "This is\na little\ntext file";
*/
printf("%s", content);
}
obtaining a little program that prints on stdout "This is
a little
text file"
At the moment I used an hackish python script, but it's butt-ugly and limited to only one variable name, can you tell me another way to do it?
I'd suggest using (unix util)xxd for this.
you can use it like so
$ echo hello world > a
$ xxd -i a
outputs:
unsigned char a[] = {
0x68, 0x65, 0x6c, 0x6c, 0x6f, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64, 0x0a
};
unsigned int a_len = 12;
The question was about C but in case someone tries to do it with C++11 then it can be done with only little changes to the included text file thanks to the new raw string literals:
In C++ do this:
const char *s =
#include "test.txt"
;
In the text file do this:
R"(Line 1
Line 2
Line 3
Line 4
Line 5
Line 6)"
So there must only be a prefix at the top of the file and a suffix at the end of it. Between it you can do what you want, no special escaping is necessary as long as you don't need the character sequence )". But even this can work if you specify your own custom delimiter:
R"=====(Line 1
Line 2
Line 3
Now you can use "( and )" in the text file, too.
Line 5
Line 6)====="
I like kayahr's answer. If you don't want to touch the input files however, and if you are using CMake, you can add the delimeter character sequences on the file. The following CMake code, for instance, copies the input files and wraps their content accordingly:
function(make_includable input_file output_file)
file(READ ${input_file} content)
set(delim "for_c++_include")
set(content "R\"${delim}(\n${content})${delim}\"")
file(WRITE ${output_file} "${content}")
endfunction(make_includable)
# Use like
make_includable(external/shaders/cool.frag generated/cool.frag)
Then include in c++ like this:
constexpr char *test =
#include "generated/cool.frag"
;
You have two possibilities:
Make use of compiler/linker extensions to convert a file into a binary file, with proper symbols pointing to the begin and end of the binary data. See this answer: Include binary file with GNU ld linker script.
Convert your file into a sequence of character constants that can initialize an array. Note you can't just do "" and span multiple lines. You would need a line continuation character (\), escape " characters and others to make that work. Easier to just write a little program to convert the bytes into a sequence like '\xFF', '\xAB', ...., '\0' (or use the unix tool xxd described by another answer, if you have it available!):
Code:
#include <stdio.h>
int main() {
int c;
while((c = fgetc(stdin)) != EOF) {
printf("'\\x%X',", (unsigned)c);
}
printf("'\\0'"); // put terminating zero
}
(not tested). Then do:
char my_file[] = {
#include "data.h"
};
Where data.h is generated by
cat file.bin | ./bin2c > data.h
You can do this using objcopy:
objcopy --input binary --output elf64-x86-64 myfile.txt myfile.o
Now you have an object file you can link into your executable which contains symbols for the beginning, end, and size of the content from myfile.txt.
ok, inspired by Daemin's post i tested the following simple example :
a.data:
"this is test\n file\n"
test.c:
int main(void)
{
char *test =
#include "a.data"
;
return 0;
}
gcc -E test.c output:
# 1 "test.c"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "test.c"
int main(void)
{
char *test =
# 1 "a.data" 1
"this is test\n file\n"
# 6 "test.c" 2
;
return 0;
}
So it's working but require data surrounded with quotation marks.
If you're willing to resort to some dirty tricks you can get creative with raw string literals and #include for certain types of files.
For example, say I want to include some SQL scripts for SQLite in my project and I want to get syntax highlighting but don't want any special build infrastructure. I can have this file test.sql which is valid SQL for SQLite where -- starts a comment:
--x, R"(--
SELECT * from TestTable
WHERE field = 5
--)"
And then in my C++ code I can have:
int main()
{
auto x = 0;
const char* mysql = (
#include "test.sql"
);
cout << mysql << endl;
}
The output is:
--
SELECT * from TestTable
WHERE field = 5
--
Or to include some Python code from a file test.py which is a valid Python script (because # starts a comment in Python and pass is a no-op):
#define pass R"(
pass
def myfunc():
print("Some Python code")
myfunc()
#undef pass
#define pass )"
pass
And then in the C++ code:
int main()
{
const char* mypython = (
#include "test.py"
);
cout << mypython << endl;
}
Which will output:
pass
def myfunc():
print("Some Python code")
myfunc()
#undef pass
#define pass
It should be possible to play similar tricks for various other types of code you might want to include as a string. Whether or not it is a good idea I'm not sure. It's kind of a neat hack but probably not something you'd want in real production code. Might be ok for a weekend hack project though.
You need my xtr utility but you can do it with a bash script. This is a script I call bin2inc. The first parameter is the name of the resulting char[] variable. The second parameter is the name of the file. The output is C include file with the file content encoded (in lowercase hex) as the variable name given. The char array is zero terminated, and the length of the data is stored in $variableName_length
#!/bin/bash
fileSize ()
{
[ -e "$1" ] && {
set -- `ls -l "$1"`;
echo $5;
}
}
echo unsigned char $1'[] = {'
./xtr -fhex -p 0x -s ', ' < "$2";
echo '0x00'
echo '};';
echo '';
echo unsigned long int ${1}_length = $(fileSize "$2")';'
YOU CAN GET XTR HERE xtr (character eXTRapolator) is GPLV3
Why not link the text into the program and use it as a global variable! Here is an example. I'm considering using this to include Open GL shader files within an executable since GL shaders need to be compiled for the GPU at runtime.
I reimplemented xxd in python3, fixing all of xxd's annoyances:
Const correctness
string length datatype: int → size_t
Null termination (in case you might want that)
C string compatible: Drop unsigned on the array.
Smaller, readable output, as you would have written it: Printable ascii is output as-is; other bytes are hex-encoded.
Here is the script, filtered by itself, so you can see what it does:
pyxxd.c
#include <stddef.h>
extern const char pyxxd[];
extern const size_t pyxxd_len;
const char pyxxd[] =
"#!/usr/bin/env python3\n"
"\n"
"import sys\n"
"import re\n"
"\n"
"def is_printable_ascii(byte):\n"
" return byte >= ord(' ') and byte <= ord('~')\n"
"\n"
"def needs_escaping(byte):\n"
" return byte == ord('\\\"') or byte == ord('\\\\')\n"
"\n"
"def stringify_nibble(nibble):\n"
" if nibble < 10:\n"
" return chr(nibble + ord('0'))\n"
" return chr(nibble - 10 + ord('a'))\n"
"\n"
"def write_byte(of, byte):\n"
" if is_printable_ascii(byte):\n"
" if needs_escaping(byte):\n"
" of.write('\\\\')\n"
" of.write(chr(byte))\n"
" elif byte == ord('\\n'):\n"
" of.write('\\\\n\"\\n\"')\n"
" else:\n"
" of.write('\\\\x')\n"
" of.write(stringify_nibble(byte >> 4))\n"
" of.write(stringify_nibble(byte & 0xf))\n"
"\n"
"def mk_valid_identifier(s):\n"
" s = re.sub('^[^_a-z]', '_', s)\n"
" s = re.sub('[^_a-z0-9]', '_', s)\n"
" return s\n"
"\n"
"def main():\n"
" # `xxd -i` compatibility\n"
" if len(sys.argv) != 4 or sys.argv[1] != \"-i\":\n"
" print(\"Usage: xxd -i infile outfile\")\n"
" exit(2)\n"
"\n"
" with open(sys.argv[2], \"rb\") as infile:\n"
" with open(sys.argv[3], \"w\") as outfile:\n"
"\n"
" identifier = mk_valid_identifier(sys.argv[2]);\n"
" outfile.write('#include <stddef.h>\\n\\n');\n"
" outfile.write('extern const char {}[];\\n'.format(identifier));\n"
" outfile.write('extern const size_t {}_len;\\n\\n'.format(identifier));\n"
" outfile.write('const char {}[] =\\n\"'.format(identifier));\n"
"\n"
" while True:\n"
" byte = infile.read(1)\n"
" if byte == b\"\":\n"
" break\n"
" write_byte(outfile, ord(byte))\n"
"\n"
" outfile.write('\";\\n\\n');\n"
" outfile.write('const size_t {}_len = sizeof({}) - 1;\\n'.format(identifier, identifier));\n"
"\n"
"if __name__ == '__main__':\n"
" main()\n"
"";
const size_t pyxxd_len = sizeof(pyxxd) - 1;
Usage (this extracts the script):
#include <stdio.h>
extern const char pyxxd[];
extern const size_t pyxxd_len;
int main()
{
fwrite(pyxxd, 1, pyxxd_len, stdout);
}
Here's a hack I use for Visual C++. I add the following Pre-Build Event (where file.txt is the input and file_txt.h is the output):
#(
echo const char text[] = R"***(
type file.txt
echo ^^^)***";
) > file_txt.h
I then include file_txt.h where I need it.
This isn't perfect, as it adds \n at the start and \n^ at the end, but that's not a problem to handle and I like the simplicity of this solution. If anyone can refine is to get rid of the extra chars, that would be nice.
You can use assembly for this:
asm("fileData: .incbin \"filename.ext\"");
asm("fileDataEnd: db 0x00");
extern char fileData[];
extern char fileDataEnd[];
const int fileDataSize = fileDataEnd - fileData + 1;
Even if it can be done at compile time (I don't think it can in general), the text would likely be the preprocessed header rather than the files contents verbatim. I expect you'll have to load the text from the file at runtime or do a nasty cut-n-paste job.
Hasturkun's answer using the xxd -i option is excellent. If you want to incorporate the conversion process (text -> hex include file) directly into your build the hexdump.c tool/library recently added a capability similar to xxd's -i option (it doesn't give you the full header - you need to provide the char array definition - but that has the advantage of letting you pick the name of the char array):
http://25thandclement.com/~william/projects/hexdump.c.html
It's license is a lot more "standard" than xxd and is very liberal - an example of using it to embed an init file in a program can be seen in the CMakeLists.txt and scheme.c files here:
https://github.com/starseeker/tinyscheme-cmake
There are pros and cons both to including generated files in source trees and bundling utilities - how to handle it will depend on the specific goals and needs of your project. hexdump.c opens up the bundling option for this application.
I think it is not possible with the compiler and preprocessor alone. gcc allows this:
#define _STRGF(x) # x
#define STRGF(x) _STRGF(x)
printk ( MODULE_NAME " built " __DATE__ " at " __TIME__ " on host "
STRGF(
# define hostname my_dear_hostname
hostname
)
"\n" );
But unfortunately not this:
#define _STRGF(x) # x
#define STRGF(x) _STRGF(x)
printk ( MODULE_NAME " built " __DATE__ " at " __TIME__ " on host "
STRGF(
# include "/etc/hostname"
)
"\n" );
The error is:
/etc/hostname: In function ‘init_module’:
/etc/hostname:1:0: error: unterminated argument list invoking macro "STRGF"
I had similar issues, and for small files the aforementioned solution of Johannes Schaub worked like a charm for me.
However, for files that are a bit larger, it ran into issues with the character array limit of the compiler. Therefore, I wrote a small encoder application that converts file content into a 2D character array of equally sized chunks (and possibly padding zeros). It produces output textfiles with 2D array data like this:
const char main_js_file_data[8][4]= {
{'\x69','\x73','\x20','\0'},
{'\x69','\x73','\x20','\0'},
{'\x61','\x20','\x74','\0'},
{'\x65','\x73','\x74','\0'},
{'\x20','\x66','\x6f','\0'},
{'\x72','\x20','\x79','\0'},
{'\x6f','\x75','\xd','\0'},
{'\xa','\0','\0','\0'}};
where 4 is actually a variable MAX_CHARS_PER_ARRAY in the encoder. The file with the resulting C code, called, for example "main_js_file_data.h" can then easily be inlined into the C++ application, for example like this:
#include "main_js_file_data.h"
Here is the source code of the encoder:
#include <fstream>
#include <iterator>
#include <vector>
#include <algorithm>
#define MAX_CHARS_PER_ARRAY 2048
int main(int argc, char * argv[])
{
// three parameters: input filename, output filename, variable name
if (argc < 4)
{
return 1;
}
// buffer data, packaged into chunks
std::vector<char> bufferedData;
// open input file, in binary mode
{
std::ifstream fStr(argv[1], std::ios::binary);
if (!fStr.is_open())
{
return 1;
}
bufferedData.assign(std::istreambuf_iterator<char>(fStr),
std::istreambuf_iterator<char>() );
}
// write output text file, containing a variable declaration,
// which will be a fixed-size two-dimensional plain array
{
std::ofstream fStr(argv[2]);
if (!fStr.is_open())
{
return 1;
}
const std::size_t numChunks = std::size_t(std::ceil(double(bufferedData.size()) / (MAX_CHARS_PER_ARRAY - 1)));
fStr << "const char " << argv[3] << "[" << numChunks << "]" <<
"[" << MAX_CHARS_PER_ARRAY << "]= {" << std::endl;
std::size_t count = 0;
fStr << std::hex;
while (count < bufferedData.size())
{
std::size_t n = 0;
fStr << "{";
for (; n < MAX_CHARS_PER_ARRAY - 1 && count < bufferedData.size(); ++n)
{
fStr << "'\\x" << int(unsigned char(bufferedData[count++])) << "',";
}
// fill missing part to reach fixed chunk size with zero entries
for (std::size_t j = 0; j < (MAX_CHARS_PER_ARRAY - 1) - n; ++j)
{
fStr << "'\\0',";
}
fStr << "'\\0'}";
if (count < bufferedData.size())
{
fStr << ",\n";
}
}
fStr << "};\n";
}
return 0;
}
This problem was irritating me and xxd doesn't work for my use case because it made the variable called something like __home_myname_build_prog_cmakelists_src_autogen when I tried to script it in, so I made a utility to solve this exact problem:
https://github.com/Exaeta/brcc
It generates a source and header file and allows you to explicitly set the name of each variable so then you can use them via std::begin(arrayname) and std::end(arrayname).
I incorporated it into my cmake project like so:
add_custom_command(
OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/binary_resources.hpp ${CMAKE_CURRENT_BINARY_DIR}/binary_resources.cpp
COMMAND brcc ${CMAKE_CURRENT_BINARY_DIR}/binary_resources RGAME_BINARY_RESOURCES_HH txt_vertex_shader ${CMAKE_CURRENT_BINARY_DIR}/src/vertex_shader1.glsl
DEPENDS src/vertex_shader1.glsl)
With small tweaks I suppose it could be made to work for C as well.
If you are using CMake, you probably may be interested in writing CMake preprocessing script like the following:
cmake/ConvertLayout.cmake
function(convert_layout file include_dir)
get_filename_component(name ${file} NAME_WE)
get_filename_component(directory ${file} DIRECTORY)
get_filename_component(directory ${directory} NAME)
string(TOUPPER ${name} NAME)
string(TOUPPER ${directory} DIRECTORY)
set(new_file ${include_dir}/${directory}/${name}.h)
if (${file} IS_NEWER_THAN ${new_file})
file(READ ${file} content)
string(REGEX REPLACE "\"" "\\\\\"" content "${content}")
string(REGEX REPLACE "[\r\n]" "\\\\n\"\\\\\n\"" content "${content}")
set(content "\"${content}\"")
set(content "#ifndef ${DIRECTORY}_${NAME}\n#define ${DIRECTORY}_${NAME} ${content} \n#endif")
message(STATUS "${content}")
file(WRITE ${new_file} "${content}")
message(STATUS "Generated layout include file ${new_file} from ${file}")
endif()
endfunction()
function(convert_layout_directory layout_dir include_dir)
file(GLOB layouts ${layout_dir}/*)
foreach(layout ${layouts})
convert_layout(${layout} ${include_dir})
endforeach()
endfunction()
your CMakeLists.txt
include(cmake/ConvertLayout.cmake)
convert_layout_directory(layout ${CMAKE_BINARY_DIR}/include)
include_directories(${CMAKE_BINARY_DIR}/include)
somewhere in c++
#include "layout/menu.h"
Glib::ustring ui_info = LAYOUT_MENU;
I like #Martin R.'s answer because, as it says, it doesn't touch the input file and automates the process. To improve on this, I added the capability to automatically split up large files that exceed compiler limits. The output file is written as an array of smaller strings which can then be reassembled in code. The resulting script, based on #Martin R.'s version, and an example is included here:
https://github.com/skillcheck/cmaketools.git
The relevant CMake setup is:
make_includable( LargeFile.h
${CMAKE_CURRENT_BINARY_DIR}/generated/LargeFile.h
"c++-include" "L" LINE_COUNT FILE_SIZE
)
The source code is then:
static std::vector<std::wstring> const chunks = {
#include "generated/LargeFile.h"
};
std::string contents =
std::accumulate( chunks.begin(), chunks.end(), std::wstring() );
in x.h
"this is a "
"buncha text"
in main.c
#include <stdio.h>
int main(void)
{
char *textFileContents =
#include "x.h"
;
printf("%s\n", textFileContents);
return 0
}
ought to do the job.
What might work is if you do something like:
int main()
{
const char* text = "
#include "file.txt"
";
printf("%s", text);
return 0;
}
Of course you'll have to be careful with what is actually in the file, making sure there are no double quotes, that all appropriate characters are escaped, etc.
Therefore it might be easier if you just load the text from a file at runtime, or embed the text directly into the code.
If you still wanted the text in another file you could have it in there, but it would have to be represented there as a string. You would use the code as above but without the double quotes in it. For example:
file.txt
"Something evil\n"\
"this way comes!"
main.cpp
int main()
{
const char* text =
#include "file.txt"
;
printf("%s", text);
return 0;
}
So basically having a C or C++ style string in a text file that you include. It would make the code neater because there isn't this huge lot of text at the start of the file.
I'm writing a larger program that takes arguments from the command line after the executable. Some of the arguments are expected to be passed after the equals sign of an option. For instance, the output to the log is a comma separated vector by default, but if the user wants to change the separator to a period or something else instead of a comma, they might give the argument as:
./main --separator="."
This works fine, but if a user wants the delimiter be a special character (for example: tab), they might expect to pass the escape sequence in one of the following ways:
./main --separator="\t"
./main --separator='\t'
./main --separator=\t
It doesn't behave the way I want it to (to interpret \t as a tab) and instead prints out the string as written (sans quotes, and with no quotes it just prints 't'). I've tried using double slashes, but I think I might just be approaching this incorrectly and I'm not sure how to even ask the question properly (I tried searching).
I've recreated the issue in a dummy example here:
#include <string>
#include <iostream>
#include <cstdio>
// Pull the string value after the equals sign
std::string get_option( std::string input );
// Verify that the input is a valid option
bool is_valid_option( std::string input );
int main ( int argc, char** argv )
{
if ( argc != 2 )
{
std::cerr << "Takes exactly two arguments. You gave " << argc << "." << std::endl;
exit( -1 );
}
// Convert from char* to string
std::string arg ( argv[1] );
if ( !is_valid_option( arg ) )
{
std::cerr << "Argument " << arg << " is not a valid option of the form --<argument>=<option>." << std::endl;
exit( -2 );
}
std::cout << "You entered: " << arg << std::endl;
std::cout << "The option you wanted to use is: " << get_option( arg ) << "." << std::endl;
return 0;
}
std::string get_option( std::string input )
{
int index = input.find( '=' );
std::string opt = input.substr( index + 1 ); // We want everything after the '='
return opt;
}
bool is_valid_option( std::string input )
{
int equals_index = input.find('=');
return ( equals_index != std::string::npos && equals_index < input.length() - 1 );
}
I compile like this:
g++ -std=c++11 dummy.cpp -o dummy
With the following commands, it produces the following outputs.
With double quotes:
/dummy --option="\t"
You entered: --option=\t
The option you wanted to use is: \t.
With single quotes:
./dummy --option='\t'
You entered: --option=\t
The option you wanted to use is: \t.
With no quotes:
./dummy --option=\t
You entered: --option=t
The option you wanted to use is: t.
My question is: Is there a way to specify that it should interpret the substring \t as a tab character (or other escape sequences) rather than the string literal "\t"? I could parse it manually, but I'm trying to avoid re-inventing the wheel when I might just be missing something small.
Thank you very much for your time and answers. This is something so simple that it's been driving me crazy that I'm not sure how to fix it quickly and simply.
The escape sequences are already parsed from the shell you use, and are passed to your command line parameters array argv accordingly.
As you noticed only the quoted versions will enable you to detect that a "\\t" string was parsed and passed to your main().
Since most shells may just skip a real TAB character as a whitespace, you'll never see it in your command line arguments.
But as mentioned it's mainly a problem of how the shell interprets the command line, and what's left going to your program call arguments, than how to handle it with c++ or c.
My question is: Is there a way to specify that it should interpret the substring \t as a tab character (or other escape sequences) rather than the string literal "\t"? I could parse it manually, but I'm trying to avoid re-inventing the wheel when I might just be missing something small.
You actually need to scan for a string literal
"\\t"
within the c++ code.