You need to toupper
every single character, e.g.
while( (leido = read(0,&buffer,sizeof buffer)) > 0){
for (int i=0; i<leido; i++) {
buffer[i] = toupper((unsigned char)buffer[i]);
}
retorno = write(1,&buffer,leido);
}
2
solved How can I use the function toupper() in this code? [closed]