Passing variable parameters to child process UNIX in c

Question

I am reading an input file in the parent and based on the content in the file, I pass them to one of the two child processes.

    char a[20],b[20],c[20];

    pFile = fopen ("instruction.dat","r");
while(!feof(pFile))
{
fscanf(pFile,"%s %s %s",a,b,c);
switch(a[0])
    {
    case 'f': write(fds1[1],b,sizeof(b));
           write(fds1[1],c,sizeof(c));
           write(1,"\nAFRCF",6);
           break;

    case 'a': write(fds2[1],b,sizeof(b));
           write(fds2[1],c,sizeof(c));
           write(1,"\nAFRCA",6);
           break;

    default: write(1,err,sizeof(err));
          //printf("\n Instruction.dat read error");
    }
}

Now, the problem I am facing is that the sizeof(a) operator returns the size of the allocated memory to the array and thus the child process receives some garbage along with the actual contents from the input file. I can't predict the size of the array beforehand so I can't use dynamic allocation (malloc or realloc) to give the exact size of the array.

What is the way to pass the exact size of strings (after reading the input file) to the write() ?

Passing exact string length to write (among a million others) seems a more suitable title for the question, just saying :) — Paulo Bu
– Paulo Bu, Commented Jan 22, 2014 at 15:41

JaredPar · Accepted Answer · 2014-01-22 15:33:39Z

3

Use the strlen function to get the size of the strings not sizeof

write(fds1[1],b,strlen(b));

answered Jan 22, 2014 at 15:33

JaredPar

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Paulo Bu Over a year ago

Hell you were fast! By the way, love your VsVim extension. Thanks for that :)

Paulo Bu · Accepted Answer · 2014-01-22 15:33:47Z

2

I think you're looking for strlen string function. For example:

write(fds1[1],b,strlen(b));

answered Jan 22, 2014 at 15:33

Paulo Bu

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