Execvp fails - (bad address)

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September 17th, 2012, 07:41 AM

Stefan1

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Join Date: Mar 2005

Posts: 399

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Execvp fails - (bad address)

Hi,
I have a problem that I have been struggling with for hours now.

I have a function which receives a string as an argument.
This string should be in the format: <programname> <param1> <param2> <etc>

The function extracts the program name and stores it in the programName array.
It also extracts the parameters and stores them in the parameters array.

It then forks and lets the child call execvp( programName, parameters ) but then the following error occurs: "Cannot execute the requested program.: Bad address".

c Code:

Original - c Code

/*
    This function tries to execute the requested program.
    It takes the requested program + arguments as a parameter.
    It returns the ID of the child process that is executing the program. 
*/
pid_t handleRequest( char* request ){
    int i=1;
    char programName[MAX_PROGRAM_NAME_LENGTH];
    char* parameters[MAX_NUMBER_OF_PARAMETERS];
    char* token;
 
    // extract program name from user input.
    token = strtok( request, " " );
    strncpy( programName, token, MAX_PROGRAM_NAME_LENGTH );
    
    // extract parameters from user input and store in array.   
    parameters[0] = programName;
    while( (token = strtok( NULL, " " )) && i < MAX_NUMBER_OF_PARAMETERS ){
        parameters[i] = token;
        i++;
    }
    
    pid_t pid = fork();
    if( pid ==  0 ){ 
        if ( execvp( programName, parameters ) == -1 ){
            perror("Cannot execute the requested program.");
            exit(1);
        }
    } else if( pid == -1 ){
        perror("Failed to fork!\n");
        exit(1);
    }
    
    return pid;
}

Can anyone see what is causing my problem? Any comments on the way I am coding this are welcome too.

Thanks in advance!

September 17th, 2012, 08:46 AM

salem

Contributed User

Join Date: Jun 2005

Posts: 3,831

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> parameters[i] = token;
You need to mark the end of the list with
parameters[i] = NULL;

You might need 1 less limit in your loop, to ensure you have space for this NULL.

Comments on this post

Stefan1 agrees!

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September 17th, 2012, 09:02 AM