is there non const variant of c_str()?

[h4ever]

is there non const variant of c_str()?

I used this to convert from string to char
const char * cpath = path.c_str();
now I found I need to trim the string but const denies to change it. So is there a variant which allows to change the variable?

[TwilightSpectre]

Yes. See http://www.cplusplus.com/reference/string/string/copy/

If you need to trim the string, why not do it while it was still a string. In fact, why do you need to turn it into a C-string anyway? Why don't you just pass the actual string object around?

[Stewbond]

Are you trying to modify the original string or modify a copy of the string?

If you don't mind modifying a copy then you'll need to copy it:

char * cpath = new char[ path.size() ];
strcpy(cpath, path.c_str() );
//...
delete[] cpath;

Otherwise, getting a char* from a std::string would be returning a pointer to the internal data. That's too dangerous for std::string because it would let someone modify the internal data without considering any other internal methods such as updating the size, re-allocating memory, etc.

http://www.cplusplus.com/reference/cstring/strcpy/

Edit: I stand corrected NT3... still the same thing, A copy is needed.

1 2

char* cpath = new char[ path.size() ]; strcpy(cpath, path.c_str() );

char* cpath = new char[ path.size() ]; path.copy(cpath, path.size() );

[h4ever]

NT3:
To answer your question, I am testing the string path:
if( stat(cpath,&s) == 0 )
stat needs char. Maybe I did not choosed correct way how to do it. My idea was to trim dot from left for the case directory name is like ./myDir , but then I realized that there can be file name like .myfile so not good idea. I should test first two characters and if they are ./ so remove 2 and add current_path to begin of the variable.

[MiiNiPaa]

stat needs char

if( stat(path.c_str(), &s) == 0 )

You should do all operation on your actual path string and convert it to c-string right before passing into function.

[h4ever]

Good idea. But I have one more problem with testing the begin of the path.

path: .\88469142758.jpeg
Type: std::basic_string<char,std::char_traits<char>,std::allocator<char> >

using:

std::string prefix(".\"");
n = path.compare(0, prefix.size(), prefix);

path.compare(0, prefix.size(), prefix);
returns CXX0047: Error: argument list does not match a function
n is 1
any idea why?

[MiiNiPaa]

compare() returns zero on match. As your string does not starts with .", it returns nonzero value. Maybe you want to compare it with .\?

[JLBorges]

> I should test first two characters and if they are ./ so remove 2 and add current_path to begin of the variable.

You do not need to do that. stat() accepts relative paths.

#include <iostream>
#include <string>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

int main() 
{
    struct stat buf ;
    
    for( const std::string path : { "./test_dir", "./main.cpp", "./../../usr/local/include", "bad_path" } )
    {
        std::cout << '\'' << path << "' : " ;
        if( stat( path.c_str(), &buf ) == 0 )
        {
            const mode_t mode = buf.st_mode ;
            
            if( S_ISREG(mode) ) std::cout << "regular file\n" ;
            else if( S_ISDIR(mode) ) std::cout << "directory\n" ;
            // etc.
        }
        else std::cout << "*** stat error ***\n" ;
    }
}

http://coliru.stacked-crooked.com/a/84653bbed9e75cbd

As an academic exercise, to get a c-style string without leading ./ if any:

    const std::string path = "./my_dir" ;
    const char* cstr = path.c_str() ;
    if( path.find( "./" ) == 0 ) // begins with ./
         cstr += 2 ; // skip the first two chars 

[h4ever]

MiiNiPaa, yes I want to compare .\ , I see my error now, should be
std::string prefix(".\\"); thanks

[h4ever]

JLBorges: But in your 2nd example if I want to join this:

const char* cpath = path.c_str() ;
	if( path.find( ".\\" ) == 0 ){ // begins with .\ 
         cpath += 2 ; // skip the first two chars       
	cpath = *workingPath + cpath; // join the value of workigPath with cPath
	}

Result is failture

[MiiNiPaa]

What workingPath is? Why do you need to dereference it? If working path a c-string too, you need to make use of strncat function.

[h4ever]

both are c string.

Edit: workingPath is c string.
Path is stiring as original.
cpath would be const c string if I use it as destination of conversation.

[MiiNiPaa]

cpath = *workingPath + cpath Here you are adding integral value of first character of working path to cpath pointer.
You need either:
1) Work with strings and take c-string as last step:

if( path.find( "./" ) == 0 ) {
    path.erase(0, 2);
    path.insert(0, workingPath);
}
const char* cpath =  path.c_str();

2) contacenate your strings:

char buffer[256];
if (path.find( "./" ) == 0) {
    strncpy(buffer, workingPath, 256);
    strncat(buffer, path.c_str() + 2, 256 - strlen(buffer));
} else
    strncpy(buffer, path.c_str(), 256);

[h4ever]

MiiNiPaa
thanks, your solution works. But I am too tired to think about is father more. Just question to the second solution. Is it possible to use similar solution but for char * buffer? But the first solution is clear and simple. Simple to remember.

[MiiNiPaa]

Is it possible to use similar solution but for char * buffer

It uses char* buffer already. You can use dynamic memory allocation and pointers to guarantee that any path would fit.