Trying to pass string variables into std::system

Question

My code:

std::string mail;
std::string password;
std::system("mkdir ~/.cache/pbt");
std::cout << "Enter your accounts mail" << std::endl;
std::cin >> mail;
std::cout << "Now enter your accounts password";
std::cin >> password;
std::system("perl zap2xml.pl -u " + mail + " -p " + password + " -o ~/.cache/pbt");

When I try to compile this code:

The compiler says

main.cpp:13:62: error: cannot convert ‘std::__cxx11::basic_string<char>’ to ‘const char*’
   13 | std::system("perl zap2xml.pl -u " + mail + " -p " + password + " -o ~/.cache/pbt");
      |             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
      |                                                              |
      |                                                              std::__cxx11::basic_string<char>
In file included from /usr/include/c++/9.2.0/cstdlib:75,
                 from /usr/include/c++/9.2.0/ext/string_conversions.h:41,
                 from /usr/include/c++/9.2.0/bits/basic_string.h:6493,
                 from /usr/include/c++/9.2.0/string:55,
                 from /usr/include/c++/9.2.0/bits/locale_classes.h:40,
                 from /usr/include/c++/9.2.0/bits/ios_base.h:41,
                 from /usr/include/c++/9.2.0/ios:42,
                 from /usr/include/c++/9.2.0/ostream:38,
                 from /usr/include/c++/9.2.0/iostream:39,
                 from main.cpp:1:
/usr/include/stdlib.h:784:32: note:   initializing argument 1 of ‘int system(const char*)’
  784 | extern int system (const char *__command) __wur;
      |                    ~~~~~~~~~~~~^~~~~~~~~

It looks like std::system can't read std::string variables and only can reads const char* , but there must be some way to do this.

How can I resolve this issue?

You should put those strings inside single quotes, as those can contain special characters or malicious script. — Akib Azmain Turja
– Akib Azmain Turja, Commented Aug 20, 2020 at 16:20

Remy Lebeau · Accepted Answer · 2020-08-20 17:14:34Z

4

std::system() takes a const char* as input, but you are trying to pass it a std::string instead. std::string is not implicitly convertible to const char*, hence the compiler error. However, you can use the string's c_str() method to get a const char*, eg:

std::string cmd = "perl zap2xml.pl -u '" + mail + "' -p '" + password + "' -o ~/.cache/pbt";
std::system(cmd.c_str());

Alternatively:

std::system(("perl zap2xml.pl -u '" + mail + "' -p '" + password + "' -o ~/.cache/pbt").c_str());

Note the mail and password strings are being wrapped inside of single quotes. This is because these two parameters can contain special characters or malicious code, and so should be escaped accordingly.

edited Aug 20, 2020 at 17:14

answered Dec 11, 2019 at 23:19

Remy Lebeau

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1 Comment

Gem Taylor Over a year ago

Note also that system calls the shell interpretter, so if the password (in particular) could contain characters that might be treated specially by the shell, even spaces, then you would need to quote it and/or escape those characters.

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