Exec fails due to Bad Address

Question

I have a serious problem with exec.I've tried both options with list(execl) and array(execv) but the problem remains.I'll give the function in which i try to make the call.

#include <unistd.h>
#include <sys/types.h>
void MyFunc(string aparams[],char* infile,char* outfile,int k,int points){

int mcount=3;
char* offset= new char[5];
sprintf(offset,"%d",k);
char* pntr=new char[5];
sprintf(pntr,"%d",points);
char* *wparams=new char*[mcount];
for (int i = 0; i < mcount; i++) {
    wparams[i] = new char[aparams[i].length() + 1];
    strcpy(wparams[i], aparams[i].c_str());
}
char *cwd; 
cwd=(char*)malloc(255); 
getcwd(cwd,255); 
strcat(cwd,"/"); 
strcat(cwd,wparams[0]);
cout << cwd << endl;
execl(cwd,wparams[0],"-i",infile,"-o",outfile,"-f",offset,"-n",pntr,"-a",wparams[1],wparams[2],wparams[3],(char*) NULL);    

cout << "exec failed" << endl;
perror("The problem in exec is:");
exit(3);

}

aparams[0] contains a string with the name of an executable file,let's say "test".I compiled -> g++ test.cpp -o test -> so I got this executable. The other positions of aparams contain some arguments for the test program.

So,test never runs(when I run it from command line it's ok) and perror shows the message "The problem in exec is: Bad Address."

I've also tried to cast all arguments(const char*) but nothing changed. Is it a problem with arguments? Or it's a matter of the executable?

What did `cout << cwd << endl;` print? – user253751 Nov 22 '16 at 01:53 — user253751, Nov 22 '16 at 01:53
It printed the expected path in which I have the file test. – JAM AICA Nov 22 '16 at 01:54 — JAM AICA, Nov 22 '16 at 01:54

score 3 · Accepted Answer · answered Nov 22 '16 at 01:58

3

mcount is 3, so wparams points to an array with three elements - wparams[0], wparams[1] and wparams[2].

Then you access wparams[3] which is invalid and contains garbage.

Don't try to access array elements that don't exist.

answered Nov 22 '16 at 01:58

user253751

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Oh..well!!! You can't imagine how many hours I've been thinking of complicated things and thought I really checked the code. Lot of thanks!! – JAM AICA Nov 22 '16 at 02:25

score 1 · Answer 2 · answered Nov 22 '16 at 02:02

Your problem is in this line:

execl(cwd, 
    wparams[0], 
    "-i", infile, "-o", outfile, "-f", offset, "-n", pntr, 
    "-a", wparams[1], wparams[2], wparams[3], (char*) NULL);

You're trying to send wparams[3], which doesn't exists! It's the 4th element of wparam array and you explicitly defined it as array[3] in the initialization of your variable mcount.

Exec fails due to Bad Address

2 Answers2