Null terminating a character pointer?

This is a discussion on Null terminating a character pointer? within the C++ Programming forums, part of the General Programming Boards category; Hello, I have a void pointer 'data' which I used to cast to a string later on by a method ...

  1. #1
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    Null terminating a character pointer?

    Hello, I have a void pointer 'data' which I used to cast to a string later on by a method that sends in another data

    Im using

    Code:
    strncpy((char*)this->data,data,len);
    How do I make sure that this->((char*)data) is null terminated?

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    Code:
    if(data[strlen(data)] == '\0')
    		cout<<"yes"<<endl;
    edit: Nope, won't work. strlen() only works on null terminated strings.
    Last edited by 7stud; 11-28-2005 at 08:22 AM.

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    What I meant was, how do I null terminate it?

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    strcpy((char*)data,'\0'); ?

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    Isnt that deprecated?

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    strcpy() only works with null terminated strings, too--that's how strcpy finds the end of the first string.

    I don't think you can unless you know the size of the array. With any C++ array, you have to pass the size around with it--otherwise you'll go out of bounds.
    Last edited by 7stud; 11-28-2005 at 08:29 AM.

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    So what do I do when my assignment says

    IOLabel &operator=(const char *data); copies the maximum of "len" character from the incoming argument "data" into the data attribute of the class. Make sure that the data is null terminated.

  8. #8
    ZuK
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    strncpy's destination string will be 0-terminated as long as the source-string is shorter then the specified nr of characters.
    To be shure that it is alwais 0-terminated you could just
    Code:
    ((char*)this->data)[len-1]='\0';
    Kurt

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    It's ambiguous, but this sentence:
    Make sure that the data is null terminated.
    is probably referring to the data member of the class. Typically, you'll use 'new' to create the memory for your member variable to store len + 1 characters. Then you copy each character from the source string into your member variable string, and finally for the last index position of your member variable string, you assign it a '\0' character.
    Last edited by 7stud; 11-28-2005 at 08:45 AM.

  10. #10
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    Quote Originally Posted by INFERNO2K
    strcpy((char*)data,'\0'); ?
    Aside from the syntax error (strcpy expects two pointers to characters, not a pointer and a char) this will cause the first character of data to be the null character, thus emptying the string. The syntax error can be fixed by doing:
    Code:
    strcpy((char*)data, "");
    Quote Originally Posted by 7stud
    strcpy() only works with null terminated strings, too--that's how strcpy finds the end of the first string.
    It only matters that the source is null terminated. You are probably thinking of strcat() which appends the source onto the destination.

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