fwrite() will do the job of fseek(f,1,SEEK_CUR)?

Question

fwrite() will do the job of fseek(f,1,SEEK_CUR)?

my code is :

while (fread(&tmp,sizeof(compt),1,fc))
        { 
            if(tmp.num == m.crd ){

                tmp.Solde-=m.mon;
                fseek(fc,-sizeof(compt),SEEK_CUR);
                fwrite(&tmp,sizeof(compt),1,fc);

            }
            if(tmp.num == m.deb){

                tmp.Solde+=m.mon;
                fseek(fc,-sizeof(compt),SEEK_CUR);
                fwrite(&tmp,sizeof(compt),1,fc);
                fseek(fc,1,SEEK_CUR);

            }

        }

• the file is a group of two struct i put them before.
• the file is opened in r+.

My problem is that an infinity loop start. when i turn on the debugger i see that the fread() gave me the second struct again and again . any help?

Answer 1

You must issue a call to fseek or rewind between read and write accesses to the same file. Fix the code this way:

while (fread(&tmp, sizeof(compt), 1, fc) == 1) { 
    if (tmp.num == m.crd ) {
        tmp.Solde -= m.mon;
        fseek(fc, -sizeof(compt), SEEK_CUR);
        fwrite(&tmp, sizeof(compt), 1, fc);
        fseek(fc, 0, SEEK_CUR);
    }
    if (tmp.num == m.deb) {
        tmp.Solde += m.mon;
        fseek(fc, -sizeof(compt), SEEK_CUR);
        fwrite(&tmp, sizeof(compt), 1, fc);
        fseek(fc, 0, SEEK_CUR);
    }
}

Incidentally, from the context elements you provide, it does not make much sense to move the file pointer by just 1 byte with fseek(fc,1,SEEK_CUR);, but it is necessary to call fseek(fc,0,SEEK_CUR); to reset the file read/write state before switching back to read mode.