Home/ Questions/How to deal with the invalid conversion from ‘const char*’ to ‘char*’ in C++ errors?
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Ambre Pruvost
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Asked: 2022-05-12T11:49:05+00:00 In:

How to deal with the invalid conversion from ‘const char*’ to ‘char*’ in C++ errors?

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I have the following cpp code, but I do not know how to find the correct result. Why has this problem occurred, and how can it be solved? This is the code I am running:

stringstream data;
 char *addr=NULL;
 strcpy(addr,retstring().c_str());
//more code
 printfunc(num,addr,data.str().c_str());
void Printfunc(int a, char *loc, char *stream)

This is the error text I receive:

invalid conversion from 'const char*' to 'char*'.
initializing argument 3 of 'void Printfunc(int, char*, char*)'on argument 3 of the function
invalid conversion
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2 Answers

  1. Best Answer
    Expert

    The cause:

    string: data.str().c_str() returns a char const*, but Printfunc() needs char*s. This is the reason of the error. It doesn’t alter the arguments, but prints them or names a file.

    This is why you might want to change your declaration.

    void Printfunc(int a, char const* loc, char const* stream)

    Solution:

    Alternativities include changing the char const* to a char*, but it is better to fix the declaration.

    Printfunc(num, addr, const_cast<char*>(data.str().c_str()));

     

    • 6

  2. string::c.str() returns a string with type const char *, as seen there

    A quick fix: try casting printfunc(num,addr,(char *)data.str().c_str());


    Although the above might work, it’s not a well-defined behavior and is potentially dangerous.

    This is a better solution: Use templates 

    char * my_argument = const_cast<char*> ( ...c_str() );
    • 13

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